A cautionary note to those using Windows beta 1 build 7000:
Several reports from users using the latest leaked build of Windows 7 indicate a potential data corruption issue using Microsoft's Windows Media Player 12.
Windows 7 beta 1 build 7000 leaked over the Christmas holidays and a Microsoft spokesperson has confirmed that there is a bug which affects the leaked build. Approximately 2-3 seconds will get shaved off the beginning of MP3s if you have set your Windows Media Player 12 settings to retrieve information from the internet and update files. The default configuration for WMP12 sets this if you use the "express" option during setup.
The problem seems confined to MP3 files that have variable bitrate. Quite a nasty bug since it quietly damages files, but that's beta software for you.