Here I wanna tell you some facts about Russian (don't be surprised) social media. This phenomenon appeared in Russian much later than in Europe and in the USA, but nowadays Russia has the world's most engaged social networking audience.
There are two main networks in Russia: vkontakte.ru (translated as "in contact") with about 14 mil visitors and odnoklassniki.ru (translated as "classmates") with about 7 mil visitors. Facebook and myspace have 2% of users in Russia.
In most companies in Russia employees don't have access to social networks (what about US?) because it effects negatively the working process.
You should be careful with your pages because your bosses or your potential bosses can use the information there to know you better. So don't put pictures of you having too much fun at a pool party or avoid writing about how much you are fed up with you work and your boss. But I guess this advice can be given not only to Russian users.
Here is some more statistics:
YouTube is used only by 1,7% of people (which is very surprising for me)
Wikipedia - 3,4% (the same)
Livejournal.com - 34,4%
Blogger.com - 1,2%
PartyPoker.com - 14,2%
Twitter - 0,9% (that is just coming to Russia)
Russian President's blog is read by almost 90 thousand people, so it's quite popular. Unfortunately I haven't found this information about American President.
And in general for me it's quite interesting to compare social network situation in Russia and in the United States. So I need to study more American social media.