Facebook - I actually deleted my first account last summer because I was kinda sick of the vibes people gave on Facebook (posting death threats as your status? breaking up with someone on another person's wall? puh-leeze.) but then I realised that my school posts more updates on Facebook than on the school site.

So in a nutshell, I wouldn't even be on Facebook if it weren't for school updates and announcements on Facebook.
Twitter - I only made one just so I could follow Tom Felton, Matt Lewis and Lord_Voldemort7. True story.
YouTube - I used to love YouTube more than my phone, but that's a different story now. After all, who wants to see "this video is not available in your country" when you just want to watch a perfectly harmless video? If that's not subtle racism, I don't know what is. They make it look like the video isn't available in developing countries because said countries mostly rely on black market, but in reality that's such a bad generalisation. It's not like I'll illegally download those videos and then sell them as if I made them just because I'm Filipino. Okay, rant over. Lately I just use it mainly for watching Nigahiga and Michelle Phan's videos.
Photobucket - I only use Photobucket to upload images I could use as avatars or signatures in certain forums. Other than that, I rarely check my Photobucket.
Others:Deviant Art - I'll be honest--I made one just so I could stalk a former crush. Absolutely mad, I know. I don't even check my Deviant Art account any longer, and I'm actually thinking of deleting my account because I really don't like the idea of sharing my art online.
Forums - I'm a sucker for forums wherein I can find people I share interests with. Sometimes I get addicted to forums. I even almost failed Philosophy class because I prioritised a certain forum over the final paper.
I still can't believe how popular Facebook is right now.
Years ago, people acted as if they'd never leave Myspace and Friendster. The thought of a Social Networking Site in which they won't be able to edit their profile background (and add background music) made them shudder. It's funny how people's opinions can be swayed so easily by bandwagon.
Anyway, I hope my answers helped your research. Good luck!
