My netbook locks up after suspending while using the battery. It happened in the former version of Ubuntu and it is happening in Ubuntu 12.04. It is most discouraging to have to reboot. Anyway I found a fix for Lucid at pcurtis.com that worked. It used the gconf-editor to uncheck 'use_time_for_policy'. But 12.04 doesn't use gconf-editor. Is there a similar configuration in 12.04?
Have you read this post? Where do I set use_time_for_policy?. It is for 11.10, but the detail may help you find what you are looking for under the bonnet of 12.04.