The Windows 7 beta will expire after August 1, 2009, and the download cap for the public version has been set to 2.5 million. As it turns out, it wasn't such a bad thing that the beta made it to the piracy networks, as users already confirmed a major bug in the beta, which was been squashed b Microsoft in time for the official release. Windows Server 2008 R2 has also been released as a beta.
OSNews already reviewed the beta earlier this week. Even though Microsoft seems to be on the right track, there are still some bugs that need to be squashed, and the company needs to make sure it doesn't do anything epically stupid that will destroy the positive image Windows 7 has in the media right now.
In any case, happy beta testing!