The latest update (which presumably you have) included a reduction in CPU usage, so it won't impact battery life at all.
My favourite is 4 finger horizontal swipes to switch between Spaces (I'm still using SL), and four finger taps to make FF, itunes, VLC, Quicktime, iphoto etc go fullscreen. But I use it for almost every App I use - Thunderbird for instance, I use three finger hoz swipes to reply (left) and send (right), or pinch out for new mail.