No, WP7 doesn't do multitasking at all. It's serial tasking - same as iOS.
Doing so without any lag, even better. True multitasking is good for a lot of things, but if it means I can't do what I purchased the phone for (talking to people) and the lag intercepts my user experience with lag or difficulties, it serves me no use whatsoever. N9 does well. Very well in that aspect. The N900 wasn't quite there because it would sometimes lag so much when a call was coming in that you'd miss the call (rotate from portrait to landscape was a killer sometimes) or you'd hit the same button multiple times in your rush (or anger) to get to the phone. ...