In kubuntu 12.04 3.2 kernel, my asus laptop, u32u, attempting to go into suspend will cause the screen to go off while the rest of the machine becomes unresponsive and requires holding the power button to force it off. Ehci and xhci drivers have to be unbinded to make the machine not lock up when suspending. http://thecodecentral.com/2011/01/18/fix-ubuntu-10-10-suspendhibernate-not-working-bug After that, suspend will only sometimes work; sometimes it will instantly wake from the suspend cycle. This occurs even after I have disabled everything in /proc/acpi/wakeup. I have not been able to determine what is causing it to wakeup, as it is random. I have tested this on the 3.4 from http://kernel.ubuntu.com/~kernel-ppa/mainline and it still occurs randomly.
Please try 3.6 when it is released it should fix a lot of these as it works around various firmware problems in laptops.
please re-open if this is still a problem with the latest upstream kernel.