WordPress 2.8.6 is out and it’s a security release so update now.
I’m expecting the usual complaints on the support forum but so far it’s been pretty sedate. I’ve been using WordPress since version 1.5.2 and I’ve never had a bad upgrade. Of course, I have a good idea what I’m doing and have never used the automated upgrade process, so your mileage may vary.
As is usual, using SVN only took me a few minutes to upgrade 6 blogs on 3 different machines.