Looks like you'd have to go back to 2006, but yes, that was the case not too long ago.

http://www.google.com/trends?q=myspace.com,facebook.com&...

Dumb question, but doesn't Google Trends cover searches, not traffic on the actual domain? Are we just assuming that the ratio of searches:traffic is pretty much the same for both sites?

Yes, you're absolutely right. I made that assumption, and justified it by seeing that Compete's numbers matched up well for the past 12 months (Compete unfortunately only goes back 1 year, hence I went to Google Trends).

That's a fair point. I still think that Facebook is in a much better long-term position than Twitter.