I'm insanely addicted to the computer and the internet... If I'm not at school or sleeping then I'm on the computer, usually. And I'll stay up extremely late on the computer, even on school days. If I'm tired I'll go to sleep when I come home from school!
There's just so many things I rely on the computer for. It's become a habit to instantly look something up on wikipedia if I don't know much about it, or to go on a music site if I crave a certain song, or even to check the spelling or meaning of a word on dictionary.com.
I go on so many web sites that I can't keep up with them, and if they don't serve a practical use for me (like file storage or something) eventually I just stop going, in favor of another site I found.
It's not uncommon for my tab bar to be full or almost full too.
Aside from all that, the internet is the only social interaction I can really get, even if I'm just reading forum posts and not talking myself. Plus any friends I have, don't live near me, so I have to talk to them online.