X freezes

Does anyone experience X freeze?

In the past month, my X stops responding sometime between 3 hours to 4.5 hours
since starting the system.  I do not know whether it is 3 hours up-time of the
system or 3 hours up-time of X.

It happens everyday and the computer does not response to any keyboard or mouse
except the power button.  As often it doesn't schedule background-fsck in the
next boot most of times, it seems that the system is still running and responding
the power button to complete the shutdown process.

Unfortunately, I didn't have a change to test if network is still responsive or not
because when I have enought time to experience this freeze, I don't have network
connections.

I've been running CURRENT and do installworld in about every 2 to 4 days.
It is Xorg 7.2.  The machine is i386 laptop.

Thanks,
Hiro