I'll preface my comments by saying that I'm not a big fan of having a multitude of OS plug-ins and application enhancers, so my system is pretty 'clean'. As far as enhancements go, I use Launchbar and Default Folder... period. I'm sorry, but it's just reality that the more third-party OS enhancers you use, the more troubles you ARE going to have down the road, no matter what OS you use... even (especially) Windoze.

I've installed 2 machines. My desktop (Quad Xeon - 12GB Ram) was due for a purge, so I did a clean install, and my laptop ( 2.4Ghz Intel Core 2 Duo - 4GB Ram) has way too many, oft' forgotten until I need them, personalization's, that I didn't want to risk losing, so I did a straight upgrade.

On my laptop I did a 'deep clean' with Tiger Cache Cleaner, along with the usual permissions repair, maintenance routines, and disk repair,and everything went perfectly. It's faster, even more fun to use, and I've had no issues (yet) with any of my main Apps (Adobe's full line up of DP and Web Apps, Microsoft Office, Parallels, Aqua Data Studio).

My desktop works perfectly... of course. As an aside, I am using IMAP on 6 different accounts and have not had any issues (once again, yet)