Social media statistics in 2010

152 millions blogs
500+ millions users on Facebook. 900 millions page-views
200+ millions users Twitter
85 millions profiles on Linkedin
2 billions videoclips on Youtube who are viewed per day.
40 millions users on Flickr
10 millions users on StumbleUpon
23 millions visitors on Digg
45 millions visitors per month at SlideShare

[source]