There's a fair bit of media that deals explicitly with trans people, some of which you may have seen or watched. Unfortunately, TV networks (etc.) aren't always as enlightened as I wish they were; furthermore, a lot of misinformation can be spread by word of mouth. Here are some corrections of common, and wrong, ideas about transgender/transsexuality.

Misconceptions debunked

All trans people have surgeries and go on hormones.
This is simply inaccurate. Many do, and many don't, for many different reasons.

All trans people view themselves as being part of a "third gender."
Same answer as the first. Some trans people say that they're third-gender. Some live quite happily as either a man or a woman. Some don't fit into either of those categories, and it'd be wise to not assume anything either way.

All trans men are very masculine, all trans women are very feminine, and all genderqueer people are completely androgynous.
Trans men can be feminine, even flamboyantly so — just like other men can! If someone identifies as a guy, that doesn't automatically mean that he has a super-macho personality. The only thing it implies is that he is much more comfortable living as a man. There is no Big Trans Rulebook that declares, "If you want to be a male, you must be a very manly male, or else don't bother transitioning."

The femininity, masculinity, and androgyny of trans people can vary widely, as much as it varies in cisgender people.

(Oh, and if you're thinking about a masculine trans woman, just switch the words and pronouns that I've used in this example.)

It's really easy to tell a trans person from a cisgender person.
Nope, not always! You've probably walked by countless trans folks in your lifetime, but the only ones who stood out to you were the ones who didn't pass (in your view) as one gender or the other.

someguy (19K) somewoman (18K)

Trans people are just "extra gay" — so gay that they "go over the edge" into the other gender.
Er, not really. The majority of gay people are quite comfortable with the genders in which they live, the genders assigned to them at birth. They may present as more feminine than the average man, or more masculine than the average woman — but, by and large, they are content cisgender people who simply happen to be attracted to the same sex.

Trans people, on the other hand, have gender identities that definitely vary from the labels that were given to them as babies.

Besides, plenty of trans women are lesbian-identified, and trans men gay-identified. Those lesbian women aren't guys who "were so attracted to other guys that they decided to become female" — they're lesbians!

Trans people are gay people who are so deeply in denial that they'd rather transition (thereby "becoming" straight in their chosen identities) than face their own gayness.
Transition would be a huge step to take just to avoid your internalized homophobia, and it's even less socially accepted than being gay is, so this logic doesn't really work out. And, like I said before, many trans people can be classified as gay or bisexual within their true, affirmed genders.

If someone is a trans woman and she likes women, why not just stay straight? It's easier.
Okay, fine, this is a question that implies a misconception. Answer: gender identity is separate from sexual orientation, as I said before. Trans women are women, and most of them do prefer to consistently live as women, and that's the bottom line. Would you tell a cisgender lesbian, "You should get a sex change, because most women are straight"? No. It's the same sort of thing.

Genderqueer/androgyny isn't a real identity. Everybody is really a man or a woman, deep down, even if they happen to be really femmey guys or butch women.
Genderqueer people do experience their identities as very real. Many of them are in quite a difficult position; while they live in a society that is profoundly two-gendered, that system just doesn't work in their cases. Genderqueerness is not just about trying to get attention, or trying to be "edgy," or trying to be part of a political movement. Neither of those two familiar choices — no matter how feminine the man's role or how masculine the woman's — is entirely comfortable for a genderqueer individual.

There are plenty of genderqueer folks, for instance, who experience emotional pain when they are called either "he" or "she." There are plenty of them who need to take a gender-neutral name, or to modify their bodies to be more androgynous, in order to stave off a pervasive sense of dysphoria.

People who don't think of themselves as male or female are just confused, undecided; they'll settle on something eventually.
As genderqueerness is a legitimate identity in its own right, it is just as long-lasting — just as integral a part of someone's self-knowledge — as any other description that people use in reference to themselves. Non-male non-female identities do not necessarily serve as impermanent states of questioning; in some people they do, and in many they don't.

Transitional surgeries and hormone therapies are simply cosmetic in nature, and aren't medically necessary per se.
Many people report that surgery and hormones have improved their quality of life enormously; without medical assistance, these people experience a very real sense of depression, and sometimes suicidal thoughts. In such cases, ostensibly "cosmetic" work is a literal lifesaver. Sure, it's true that these treatments do alter the surface of the body, which is what many trans folks are looking for. However, they can often improve a trans person's emotional state as well (sometimes dramatically!) in a way that cannot be duplicated by any other method. Other folks, of course, get along very well without it. Depends on the individual.

Transgender/transsexuality are not accepted as valid conditions by prominent scientists; that is, people may claim that they're members of [gender], but they'll really be members of [sex] all along.
It's true that people can't change things like genetic makeup, production of sperm vs. eggs, and so forth. That doesn't happen. But it is a general consensus within psychological communities, and backed up by some scientific evidence, that trans people do exhibit "masculine" or "feminine" behaviors distinct from the typical traits of their physical sex. There are a number of interesting books and articles that deal with this subject: searching for "transgender" in academic databases can yield a fair bit of information.

Trans people all share a particular value system . . . share a political ideology . . . share a certain set of ideas about gender.
There is one thing that all trans people definitely have in common: they're trans. That's the one thing. Politics and philosophies vary, as in other human populations. Not all people with diabetes agree on things, not all librarians agree, not all gay people, etc. There's no reason why that should be different for trans people.

Trans people are buying into the false idea that there's some ultimate abstracted difference between male and female. They're essentialists. If they were really enlightened about gender, they would feel comfortable just being "people," without identifying themselves as "men" or "women" or anything. And then they wouldn't need to transition.
This sort of comment neglects the actual experience of being trans, instead choosing to focus on pure theory. Living as a man (male body and/or presentation and/or social role) is very different from living as a woman (ditto). And both of these are quite different from living ambiguously or in-between.

That's the way it is. When people experience discomfort with their bodies, when they consistently feel happier with a certain balance of hormones in their system, when a particular pronoun keeps opening some painful wound of dysphoria . . . That's real emotion and genuine self-ness, not some sociological construction. It's what a person is inherently, and it doesn't go away by sheer power of thought.

If people don't immediately disclose that they're trans, that means that they're lying or being deceptive. It's only fair that you tell people you "used to be a man/woman"; it's dishonest not to mention your transition, particularly if you don't even talk about it with close friends or sexual partners.
The first correction is easy: a trans woman (for instance) didn't "used to be a man." She may have lived in a man's social role, her sex at birth may have been classified as male, but that doesn't mean she's ever been a man. It means she's a woman who was miscategorized.

Secondly: some folks are very open, freely discussing almost all aspects of their lives, including gender stuff. Some happen to be quieter or more selective. But remember the refrain — there's not just one right way to be trans.

Omitting mention of their histories can feel like "hiding" to some trans people, but others prefer keeping the information to themselves, for a variety of reasons. People may think of you differently after you disclose. They might scrutinize your behavior, talk about you behind your back, or exclude you socially. And it's not like people have a right to know, anyway; privacy is privacy. For these reasons, and a lot more, it's perfectly reasonable for people to not mention they're trans.