This applies equally well whether you have Fedora 10 or Ubuntu, if your Compiz or KWin window managers are "freezing" (yet you still hear music play, the cursor moves erratically and the keyboard responds sporadically).
The lockups are usually when you interact with your window manager in some form that uses the 3D capabilities of the card, such as animating windows, using the cube or the enhanced zoom feature on Compiz. Other symptons are random lockups when runnign 3D apps such as glxgears. And, finally, you might experience data corruption on your hard disk (I did!).
The quickest way to "unfreeze" it is to kill Compiz or KWin through an SSH remote connection (it might also work if you switch VTs to a text terminal and then killall -9 compiz kwin). But that won't cure the freeze -- the minute you reopen your graphical session, it will return.
The definitive cure is simply to upgrade to the latest beta version of the NVIDIA driver (in this case, specifically the version 180.18 beta).
This worked for me (I have a GeForce 8800 GT, but others with 8600 or series 7000 cards may also see the problem solved. This doesn't solve the problem completely but it turns 5 minutes with Compiz into several hours.
Props to Deanjo on #compiz in FreeNode for the tip.