HD7 .. forget multitasking but the usual scenario was that even locking the screen resulted in the app having to load from scratch. Thats just a single scenario. In my usage time , even music playback didn't work properly while multitasking.
I was using a proto however so maybe stuff has improved... what i mean to say is that since it is quite a substantial investment, a person should try it out once before spending quite a lot of money. I am not judging the OS , but just warning prospective buyers to make a cautious decision about this still nascent OS.
I actually want to quote what the CEO of a pretty major mobile manufacturer told me ... " Microsoft made Kin , look what happened to it. With Win 7 , its best to wait and watch their game over the next 6-8 months and then make a decision"