Comment 18 for bug 489360

superseba, I would suspect your Intel iwlagn kernel module is the culprit. You got some suspicious entries in the kernel log you posted earlier. The driver is known for doing some dirty things. Look at this http://forums.opensuse.org/pre-release-beta/424730-bug-intel-wireless-module-freezes-machine.html I would also suggest searching for problems associated with iwlagn on google.com as well as here.

If freezes happen quite often, you could try disconnecting your wireless and just using wired connection instead. You can do it from by rightclicking your nm-applet and/or unloading the iwlagn module. You may also try finding an alternative to that wireless driver . In may case, I had had frequent system freezes due to a bug in the ath5k module and switched to ath_pci module instead.
good luck