Avatar construction is probably the most fun, yet least thought out part of roleplaying. For my own part, I usually write up a blurb or two (or at least ruminate) on the personality of the character and how some of those traits might manifest themselves in within the (often limited) scope of personalization options given in the world. Some worlds such as Second Life permit enormous versatility, whereas games such as Everquest 2 are sadly much more limited in scope.

Perhaps one of the most difficult parts of personality related to avatar construction is the notion of gender assignment; to wit, is the gender of the player the same as the gender of the avatar? The running gag in most roleplay circles is that the person behind the keyboard is a male, mid - 40's, overweight stockbroker who lives in his mothers' basement and likely has never felt the touch of a woman. While I'm sure this is somewhat true, modulo a few criteria, given the gender ratios observed in most MMOs (particularly Second Life), I'm inclined to quote Bartle in Designing Virtual Worlds (2003):

[Virtual worlds] are not worlds because they are worlds; they're worlds because people think they're worlds. What's more, players think these worlds are not the real world.

What troubles me immensely though is the number of so-called roleplayers who don't think the virtual world separate from the real world.

Another good example would be Gorean roleplayers in Second Life. My own experience with them has been a majority that extend their master/slave philosophy to the player roleplaying the character, which in my mind is more akin of a "lifestyler" than a "roleplayer". In my mind, a key part of roleplaying is keeping one's out-of-character out of the in-character behavior.

The increasing prevalence of voice-chat systems like that embedded in Second Life or Ventrilo, while useful for coordination and socializing, seem to me to really defeat the purpose of cross-gender roleplaying and identity exploration through roleplay. This seems an awfully high price to play, isolating out the fringers, the confused, or the truly dynamic roleplayer wishing to get outside the box.