Just picked up a refurb Mini that came with the SL installed and the Drop In disc. I did an erase and install of a full backup of my old machine from an external drive, reinstalling SL afterwards. Performed usual voodoo before and after backup install and SL upgrade, and the 10.6.1 update.
Everything seemed fine, but had some strange Airport behavior so called Tech Support. Seemes there was indeed a problem somewhere, so reverted the Mini back to 10.5.8. Just for grins I also installed SL on an Air running 10.5.8 and had the same Airport problem, could only access the base station with one certain configuration that was different from 10.5. Don't use the laptop that much, or for heavy lifting, so haven't explored SL further on it.
In the meantime I did a bit of research and found lots of folks having Photoshop and printing problems with SL along with the usual teething situations, mostly involving haxies and drivers. During a call about another matter, an Adobe tech support person recommended that waiting 'till 10.6.2 "would be a good idea". This was also echoed by some of the more knowledgeable folks posting on various forums.
Always a good idea to check for compatibility with necessary apps and equipment before making major OS upgrades and make sure to bring everything else up to current standards afterwards.
BTW - incompatible components found by SL are moved to a folder on your hard drive labeled "Incompatible Software"