There is a problem if you point the external plugins folder to the PS6 (or even PS7) native plugins folder - Adobe recommend using a separate folder for third party plugins (I've long used Program FilesPlugins, but that's so I can easily share with Painter) but of course some insist on going in the PS folder, so those would need reinstalling to CS (if they still work, of course. They took out the thumbnails in CS for Windows - they were just unable to get the icon handler to play well with Windows (I'm sure you've had occasions when a PSD has suddenly started to show the icon for another application, the Intellimouse being a favourite of my system). It is, I believe, possible to hack the Registry to use the earlier routines: see the Adobe User-to-User forums if you dare.