While I was trying out the new Safari 3 (Public Beta) browser, I really missed mouse gestures that I have been using in Firefox for a long time (and which I cannot do without!).
However, adding mouse gestures to Safari (and all other Mac applications) turned out to be quite simple. The shareware program xGestures makes it possible to define gestures for individual programs and map them to useful functions.
After defining various gestures (e.g. Back, Forward, New Tab, Close Tab), Safari became quite useful but I still prefer Firefox because of the massive amount of indispensable Add-ons available.