Adobe's implementation of multitouch features in Photoshop CS4 for Mac is very annoying… although multitouch 'pinch' zoom is useful, the multitouch rotation, which is extremely sensitive, isn't.
When you try to zoom (or even if you're accidentally touching the trackpad with two fingers) Photoshop often rotates the canvas by a few degrees or more — and there seems to be no easy way to set it back to straight without painstakingly using the multitouch rotation tool again. In short: this "feature" really gets in the way of getting work done.
If you find this annoying, like I did, you can download a plugin that Adobe has made available that disables multitouch functions in Photoshop CS4.
http://www.adobe.com/support/downloads/detail.jsp?ftpID=4337
To install it, open the disk image that downloads, and drag the plugin to your Applications > Photoshop > Plugins folder, and restart Photoshop.
Unfortunately it disables ALL multitouch actions, so you lose the multitouch zoom as well, but in my opinion getting rid of the annoying multitouch rotate is a greater advantage than the loss of multitouch zoom.
