I used them back in iOS 4 by enabling them through Xcode and loved them. I was sorry to see them go in iOS 5.0, and was happy to see them return in 5.0.1. They're just like I remember them
I did the same as above, and enabled through Xcode. When they went, I had to go back to using the bloody home button. When it first came out, the home button was Ok. Now it seems very inelegant, and as time goes on you wonder at what point it will fail.
These gestures are not well configured for iPod and iPhone, due to the small screen size. there is an app in cydia (must be jailbroken) called QuickDo, more tweaks are available.