-I restored my AppleUSBMultitouch.kext back to the default 10.5.6 prior to installing 10.5.7. IT looks like it has an incremental update (has the number changed). I wonder of the four finger gesture hack still works?
I didn't restore mine to the default version before updating. When I updated it automatically removed the 4-finger gestures.
This page has instructions on how to do the 4-finger hack, although it may not work on 10.5.7. I'm going to wait for someone else to try it first.