Multi-touch gestures are a great way of gaining valuable seconds when you're in a rush, and they're really easy to learn.

As well as your standard Apple gestures (e.g. pinch zoom), there's a few 4-finger gestures:
1) Return to the home screen - do a 4-finger pinch
2) Switch between recent apps (ones that appear on your multitasking bar) - swipe 4 fingers horizontally
3) Hide/show multitasking bar - swipe 4 fingers up to show the bar and down again to hide it

These can all be done using some steps involving the Home button, but it's personal preference and I find this quicker and easier to use (although I use the Home button for screenshots). This could also see a redundancy for Home buttons emerging in future.