So looking at upgrading my 3.5 install to 3.9, but wanted to see if there's anything to be particularly concerned about. I don't want to hose everything accidentally.
Anyone have horror stories to share?
Not really - you might fiddle a littlebit with the BoingBags 1 and 2, but with a more or less "normal" system it should work. My systems are running AmigaOS3.9BB2 with MUTools since years and very stable.
My personal view is: If you use OS3.x, then use 3.1 or 3.9, but never 3.5! ;-) OS3.9 ist what 3.5 should have been - I upgraded and never looked back.