Here's what Microsoft has written in the Windows 7 Beta Release Notes regarding MP3 files:
"When MP3 files are added (either manually or automatically) to either the Windows Media Player or the Windows Media Center library, or if the file metadata is edited, several seconds of content may be permanently removed from the start of the file. This issue occurs when files contain thumbnails or other metadata of significant size before importing or editing them.
To avoid this, ensure that all MP3 files that may be accessed by a computer running Windows 7 (including those on removable media or network shares) are set to read-only. To do this, in Windows Explorer, find the files, right-click them, click the General tab, and then select the Read-only check box. Then back up all of the MP3 files prior to using Windows Media Player or Windows Media Center.
If some of your files have already been affected, you may be able to recover the data by using the Previous Versions feature. To do this, right-click the file name, click Properties, click the Previous Versions tab, and in the File Versions pane select the most recent previous version."
So going through this procedure to select all MP3 files to make them Read-only could be a major hassle for someone with a mix of MP3s, WMAs, FLACs and AAC files. In my case, I have everything organized by artist, albums and tracks. All tracks in an album use the same filetype, but not all albums were encoded with MP3s. Unless you've got your folders organized by filetype it might take a long time to go through a music collection to modify their properties and backup everything.
Since the warning also applies to MP3 files that are stored on network shares, I think I'll hold off for awhile before installing the Windows 7 Beta. While listening to Microsoft's CES keynote, if I recall correctly, it sounded like Steve Ballmer said they were going to open up the beta for the public today (Friday). If you decide to install the Windows 7 Beta, I'd love to hear back from you if you figured out a good way to protect your MP3 files with minimal hassles.