COOL UPDATE: Just found this out, you can actually play your Live Mesh Music Collection for your Live Desktop within the browser! Its using Silverlight to stream the music.
As I popped out for my Lunch Break this I decided to buy the latest Weezer Album from my local JB Hi-Fi store. I have a work and home PC and normally I would have to Rip the album two different times into two different libraries which I find annoying. I have a Music Folder on my Live Mesh on my work and home PC's which I have added to my music library in Windows Media Player.
I changed my Ripping location to my Mesh Music Folder on my Work PC.
After I Rip the album I can see the little Live Mesh Icon in the tray flashing indicating its uploading the album to my Live Mesh.
When I get home and load up Media Center, Weezer is ready for me to go. Very nice.
You're not going to load up your whole music collection because the Community Technology Preview has a 5GB limit but its great to have a couple of gigs of music on your Live Mesh so you can access it from anywhere.