Almost a year and a half ago, Infochimps, the data repository slash marketplace, released a giant scrape of Twitter data representing 2.7 million users, 10 million tweets, and 58 million connections. Twitter soon requested that they take it down while they figured out how they wanted to handle licensing, privacy, etc.
That was in 2008, before Twitter really started booming. Fast forward to now. Twitter and Infochimps have figured out what they want to do, and the Twitter census data is back up. It's no longer a measly 2.7 million users anymore though. The population has grown to 35 million.