Zero Punctuation first sparked my interest in this site, back when the videos were first airing on YouTube and occasionally G4, and I thought this place'd be a great place to visit and talk about all sorts of gaming-related business. This place is a wonderful alternative to the Gamefaqs and IGN forums, and plus we're free to talk about non-game-related stuff, provided it's in the right place.
As for why I post, it's a combination of options 1, 2, 3, 4, and 5. Mostly 2 and 3, and definitely 5.