yeah a lot of the ones supplied by Adobe migrate upwards fine, some of the 3rd party ones do okay, others require an upgrade... especially when the newer version of PS entails a revamped engine like they did with the brushes in ver7.

best thing to do is to test them out and see. i know KPT had some issues with PS7 and people still using KPT3. the UI would "hang" on certain filters and you needed to "esc" out to release the program...

just my additional 2c,
:)
retrocity