Apple earlier today released iTunes 10.5 final version publicly for Windows and Mac. Now, they have seeded iTunes 10.5.1 beta with iTunes Match Beta to the developers and is available to download for them.
iTunes 10.5.1 beta has been released to the developers with the aim of testing the upcoming iTunes Match service.
This was the release notes regarding this update from Apple :
iTunes 10.5.1 beta 1 includes several performance enhancements and bug fixes, and is a required update for all subscribers to iTunes Match beta. iTunes Match is not included in the iTunes 10.5 GM release
Your iCloud libraries will be deleted at the end of this beta.
Backup regularly and do not delete the music you add to iCloud from your computer. Apple may periodically delete all iCloud libraries during the beta period. This will require you to scan, match, and upload songs again. Also note that some of the features and optimizations of iTunes Match may not be available during this beta.
Download iTunes 10.5.1 Beta With iTunes Match Beta from the dev center