It's not just me then - thought maybe I was losing it. (But I also absent-mindedly try gestures on my crappy mouse on my Dell at work, too. Hard to break a handy habit.) I kept looking at webpages and trying to swipe back to no avail. It's a little odd that they've implemented at least the finger-swipe back gesture in iBooks but not anywhere else. It would obviously have to be different in other apps, since one finger would move things, but I think most people would get it. I hope it is being added in 4.0 - maybe it's not in 3.2 just to make iBooks stand out in particular and show what gestures really can do.