I've played both as a boy and a girl (flare is a girl!) on Runescape and the differences are obvious.
For one, you are MUCH more likely to get dissed/insulted/picked on as a boy than you are as a girl.
Where girls are much more likely to be bugged about "gf" crap...
Boys are expected to have stupidly high levels and if you do have those levels expect a lot of "haha my main has 950 combat and 2058375 woodcutting"
Girls on the other hand tend to get the "OMG you're teh godly" treatment...
You *quickly* find out who's nice and who isn't as a girl because it takes a lot less time for horny teenagers to break to the graphical sights of "jiggling" and go "I LOVE YOU". If someone doesn't do this for a week-month they're usually just talking to you because they like you as you are not because your graphic jiggles!
(I say teenagers but I really mean the mindless kids...)
As a boy you're more likely to have a little more fun with the sexual inedeuo or however you spell it. Whereas girls tend to be "freaky" if they even join in unless they're very careful in their choice of words... Weird but true...
Girls also get a crapload of free stuff...usually for no reason but just for being a girl in the game. I notice that most people do this particulary to girls with good "spoken" english as opposed to girls who speak in "gangsta" and show off a tomboyish vocabulary "Ya! teh r0x0rz my b0x0rz" sort of stuff...
Overall I prefer being a girl in game. If i'm not in the mood for the "gf" crap I block the kids (who's numbers are fewer in members). People seem to be more friendly, less competetive and more respectful in general although not always. And it beats being bugged for levels and then getting the same "OMG I OWN j00" crap that just floods me on my old male character...
That's me, hope it gives you some idea of what i've seen.
