Have problems getting hibernation to reliably work. Today, instead of hanging I actually got an error: "Insufficient system resources exist to complete the API."
Googling on the error gave Q330909 and Q909095 as relevant KB articles. The former refers to an issue that was fixed in SP2, while the latter is available as a hotfix. Given that I have 4GB of RAM installed (approx. 3GB available to 32-bit Windows) and that I do tend to chew through it (commit charge peak is currently 1.3GB after a few hours of runtime), Q909095 looks likely as the solution. I've not seen this with Hector, most likely as it never had more than 1.5GB of RAM.
Update: Have installed hotfix Q909095, and it appears to work. Won't know for certain for a bit of course, that's the trouble with intermittent errors.