CS1 has better 16-bit support than 7 if that floats your boat. It did for me till I gained the ability to run Wilbur. Now I do most of my high-bit greyscale editing in Wilbur and mostly just do the 8-bit rgb stuff in PS. I still use CS1 exclusively for two reasons: 7 doesn't seem to run in OS X 10.5, I still can't afford the $300.00 to get the academic version of CS4. I've really been looking forward to Smart Filters and now I want Smart Objects.