A lot of kids create alter egos. I think for some kids that release is excellent. But there is the worry that these are society's ideals and when kids claim these ideals to describe themselves to others, they are rejecting something important about themselves. There's the Spice Girls and Hanson, which inspire such passionate love or hate that some chat rooms have had to ban discussions of relative merits of the two groups. The movie Titanic seems to be universally adored.
Kids are interested in discussing the sports they play.
The weather is a popular topic, too. But to even the casual observer, it quickly becomes clear that for many kids, the main attraction of cyberchat is the opportunity it provides for meeting members of the opposite sex. Experimenting with dating seems to be as important as experimenting with identity. You can try on the idea of having this person who is supposed to be special without having this very scary physical aspect. The safety of a relationship conducted via modem allows kids to be less timid than they would be in real life.