I use the four finger functionality all the time, with the exposé. Much easier than the old ways to quickly switch programs and get an overview of whats running.
I wish you could customize it a bit more though. Like using the zoom-function for pictures on webpages as well.
The design is great, I'm all for less buttons, BUT!.. I thought they would make it much better than it is. I heard the whole thing was going to be a button, and thats not the case.
It's way too hard to press it on the upper part. And really, the resistance of the button varies all over the pad, which is not good. I also don't like the clicking itself. It should be much smoother, like joypad buttons.