Quick experiment I just did to see when Googlebot crawls a new page on an established domain. No other inlinks, this page lives in its own new directory.
Post to twitter (not using bit.ly but the whole URL), from a 600 follower account-- immediate hit from Googlebot as well as a Google App Engine bot.
Post to established but fairly inactive blogger account with link in title, immediate hit from Googlebot.
Post to Facebook with large account (1000 friends)- nothing from Googlebot (not surprising, privacy settings are tight on this account).
Maybe this is obvious stuff to most, but it's pretty fascinating to me (especially the Twitter indexing, but it makes sense as immediate indexing is basically the only way they can add any value to Twitter search).