I had Grooveshark on my HTC Hero and I have heard that you can have it on jailbroke iPhones, if this is true do you still need to pay for a VIP account please ?
Also I have had a we7 trial on my iPhone and its pretty impressive especially the offline playlists feature :), whilst at home on wifi you can just go and select some albums you would like for that day then it will put them into offline mode and you can listen to them all day as if you own them.
One dis-advantage is the apple "switch between tasks more easily, but we close some of them first" that they like to call multi-tasking, as you can listen to music on we7 whilst doing anything else
What are your thoughts ? also can a spotify account be shared ?