I exported Twitter, Facebook, Google Plus, LiveJournal, WordPress and LinkedIn to find out. (And even found an archive of Google Buzz.)
I checked out what you get when you export your content from Twitter, Facebook, Google+, LinkedIn, WordPress and LiveJournal, with an eye for both private archives and migrating to your own site.
@trwnh I just finished a comparison of various social networks’ exports. Weirdly, LinkedIn was the most complete.