I'm not a fan of gestures that use more than two fingers -- I find it hard to hold down three or four fingers on the screen at the same time with enough pressure for them to register. Three is hard, and four is totally imposssible -- my little finger is a lot shorter than my other three fingers, it just doesn't feel comfortable to have to put all four fingers down on the screen at the same time.
So what I'd like is something like hold on the screen with two fingers to go into switcher mode, then swipe right or left with one finger to switch apps, like in the Palm Pre. But whatever they do, having to hunt for the home button in order to switch between apps is more awkward on the iPad than on iPhone/touch, because you hold the iPad in all four directions, so you never know where the home button is at any given moment.