I have Kubuntu Gutsy and have just recently enabled Compiz.
I've found that it runs fine for days unless I start Amarok playing.
Amarok will happily play for about an hour or two and then the system will suddenly log me out entirely, showing me the kdm log in screen.

The folks on #compiz-fusion don't seem to know what the problem is so I've come here to ask if anyone has had a similar experience with Amarok, or if not, has any idea how best to trouble shoot this strange problem?

~/.xsession-errors doesn't seem to contain anything notable.

This means that your x-server (Compiz) is actually crashing. So it's likely some sort of Compiz or driver bug.