I took a moment last night to figure out why my laptop sometimes resumes from a suspend and sometimes doesn't. It seemed to work so well for quite a while that I was very surprised when it begain failing on a regular basis.
The culprit was the wireless card. It's a Netgear WG511 that I got from Circuit City (*yuck*) about a month ago. Once I started thinking about it, that's about then resuming stopped working. Imagine that.
The solution is to pop the card out before suspending the laptop. Really, I don't think that's such a problem. When I suspend I'm usually about to tuck the laptop into its case at which point the card has to be removed anyway. Hotplug works great when I pop the card back in, so no big deal. This one turned out a lot easier than I expected.