Apple has just release iTunes 10.5.1 Beta 3 for developer with the integration of iTunes Match. This version improves performance and stability but seems like it is something to do more with iTunes Match. Now Apple is preparing the way it will work with iTunes Match for better result.
What Is iTunes Match?
iTunes Match is a service which stores your music on iCloud. It will scan your library music with those you have purchase from iTunes to see if there is any music are the same. If they are the same, iTunes Match will skip it and will only upload the one that do not appear on iTunes. It saves your time.
However this service is NOT free. You have to spend $24.99 per year.