more vista woes - not sleeping

My latest Vista on MacBook Pro problem is that it's not sleeping on lid close consistently. This morning when I arrived at the office and pulled my MBP out of the bag, the fans were all running full-blast, the shell was almost too hot to handle, and my battery was half drained. Apparently when I closed the lid and stuffed the machine in its bag at home about an hour earlier, it didn't actually go to sleep like it was supposed to.

I tested it a few times during the day and three out of four times I closed the lid, it went to sleep within about 10 seconds. One time, however, after 30 seconds it still wasn't sleeping and I opened it to see that everything was still running.

If anyone knows what's going on here, I'd appreciate the help.

Photo by Flickr user julian- and used under a Creative Commons license.