Comment 7 for bug 44393

Uhm. Have you tried modifying the /etc/default/acpi-support file? Because out-of-the-box it is misconfigured (I am assuming that the Dell does have a Nvidia card, but it might affect machines without it; I have tested it only on my Dell Inspiron 6400). In order to get it working, you have to modify the file.

I attach here my own, try configuring yours following my modificattions ;) I do get suspend working, however hibernate does not (but I never use it anyway).

Also, pm-utils fixed this. The only problem, when you pm-suspend Networkmanager will crash (and will have to be shut down and reactivated by hand), otherwise it'd work fine, while pm-hibernate works like a charm (but since I get acpi-suspend functioning, I am sticking to acpi ;) )