Right now while Google Music is in beta its free but after the beta no one know if Google will charge for this service. but im Brett sure it will be free like most all other Google service. Google also give you some free music when you get your invite. But Please Remember This Not A Backup Service and You Can Not Redownload The Music To Your Computer Or Any Device's. Google Music also work on iPad browser too.
This Serivce Right Is US Only
Check Out http://music.google.com