A fantastic working and looking Google Music web app has just been released for iOS. Open http://music.google.com in Mobile Safari and off you go. It even works when you hide Safari and use other apps. Google Music has been of my favourite and most used web apps in the last months.
(I have 2 invites for Music beta to give away. Please mail me your email address associated with your Google Account, if you’re interested. It works in Germany.)