Yeah, they're very interesting. I have to say though that I find the way they flick in and out of existence as the section header itself moves on and off screen a bit distracting. I'd have gone with something a bit more like iOS sticky scroll list dividers--on a lot of iPhone list widgets, if there's a header in the middle of a scrolllist, it sticks the top of the screen as you scroll past it (until you hit another one). Not sure how exactly you'd do this in a sidebar tho....