I had almost the same issue as you did on my Dell Precision M90 --- for me, hibernate didn't work, although suspend did. I found this alternative to the suspend/hibernate mechanism built into Gutsy: http://blog.paulbetts.org/index.php/2007/02/11/fixing-software-suspend-hibernate-with-uswsusp-in-ubuntu-feisty-and-edgy/

The alternative (uswsusp) works well for me.