On many ASUS laptops and probably on some non-ASUS ones you need to unload
ehci_hcd or unbind both USB controllers from it before entering S3, else
the system will lockup. Here are some links:

http://thread.gmane.org/gmane.linux.kernel/1222803
https://bugzilla.kernel.org/show_bug.cgi?id=37632
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=658778
http://ubuntuforums.org/showthread.php?t=1444822

This still happens on my K53E on v3.4-rc2-16-ga9e1e53.

Unbinding just one of two controllers doesn't help.

Disabling /sys/bus/pci/devices/0000:00:1[ad].0/power/wakeup doesn't help.
echo mem>/sys/power/state doesn't hang with 'core' in /sys/power/pm_test,
only with 'none'.

Windows 7 enters S3 perfectly well.

I didn't see any other suggestions how to debug this. I can provide any
debug data if that will help. This seems to be a very important problem
for owners of certain devices.

-- 
WBR, wRAR