I’ve use automatic plugin update just fine for WordPress 2.8, 2.8.1 and 2.8.2.
What I have found, just now, upgrading WordPress itself to 2.8.2 using automatic update, was that I could upgrade one blog only. The next blog would get stuck trying to upgrade. However, when I returned an hour later, it worked for the second. I’m hoping it will work for the others too pretty soon.