Panda isn't exactly a penalty - it's re-ranking done by a major new component in the total Google algorithm. So I don't think there will be any "return", at least not the way we've seen a return when a penalty is removed.
You're right that no site has perfectly "returned" but there are a few I've heard of who are now seeing a lot more Google traffic, up to 75% of their pre-Panda levels. That traffic has a different keyword "shape" than it did before, but it's there.
I think the way that traffic returns (where it does) is going to tell us something more about Panda, over time. But it's too early... way too early. A number of Google-watchers feel that user metrics play a big part in Panda. If that's the case, then there may well be a long delay while user metrics show the kind of signals that Google is comfortable with as signs of quality.