Whenever I fire up my laptop, I have to be careful, because of the above problem. Now, ever since I have got Direct Rendering with my ProSavage chipset working, I've had that kind of problem with my laptop, since 2.6.11 to 2.6.15. Since then, I've switched from Gentoo to Ubuntu, and I can tell you the problem hasn't changed at all.

As I run the kernels over and over again, I think the freezes become more frequent. Then, I get frustrated and recompile my kernel (without issuing a make clean and mad optimization flags, it doesn't matter either way), and when I do that, the freezes diminish. Then after I run the kernel a lot of times, the freezes become more frequent. At least, that is my feeling for what is happening here.

I run X11R7.

Established: The freezes have nothing to do with kernel Savage DRM, or AGPGART. This is because I compiled another kernel without those options, and it still freezes.
Established: The freezes do not occur when X is not running, although when X is running and I am in Ctrl-Alt-F1, for example, it will still freeze after some time.
FOOD FOR THOUGHT: It used to freeze after some time even when X was not running in Gentoo, even when I wasn't even logged in. However, I don't think I have experienced that with Ubuntu. Perhaps it is because no console app in my Ubuntu system is linked against X, unlike my Gentoo version of links, which wouldn't run if X was not installed.
Established: The system usually freezes when there is heavy disk activity, for instance, running dpkg --configure -a after a botched install. Tried compiling my VIA chip driver as a module. Did Not Help. Will not remove my VIA chip support from the kernel.
Established: I don't think the system crashed when I used the vesa driver for X.

I hope you guys will help me out and give me further places from which to troubleshoot, because once the laptop freezes I am unable to quote any system logs or kernel messages. So sorry, no informative messages here.

run memtest86 on it, its on the ubuntu cd i believe. Sounds like you may have a RAM problem. That exact thing started happening to me once.

I ran memtest86+ and cpuburn on the laptop for 24 hours each, no errors reported. I'll run it again tonight just to be safe...

as I said it's just an idea ....

you might have a heating problem, hard drive,vga processor some of the bridges (slim possibility) or maybe the cpu ... after some abuse it heats up and crashes .... try check the temperatures on each of the above....

hmmm... maybe I have to add some more ESTABLISHED points.

ESTABLISHED: I have run the laptop compiling stuff for days on end without crashing.
ESTABLISHED: It crashes in the amount of time it takes for me to boot, start gdm, log in, and execute quake3. At which time, it is barely warm.
ESTABLISHED: I have run the laptop on my friend's bed at a stayover, and it can get scalding at times, but it didn't crash.
ESTABLISHED: I always turn on the fan whenever I turn my laptop on.

Just some food for thought, because if anything, it sure isn't the overheating. That thing almost burned me once! And it still ran. It still ran.

VIA C3 933MHz
VIA PN266
Fujitsu MH something 30GB
256MB DDR266
ProSavage DDR integrated graphics

I have a Via C3 based PC that freezes with Ubuntu Dapper. I've googled around for hints, and I've found these:

1. Try running 'chkconfig cpuspeed off' to disable this service.
2. Add 'alias longhaul off' to /etc/modprobe.d/aliases

Haven't tried it myself yet.