As I understand it this will be a slimmed (slimed?) down version of CS3 and probably won't run properly on anything older than Intel CPU and OS 10.5.(yawns & exit right)

(momentary return stage left)
However it would be interesting to know if it includes curves and whether (on mac) the preview quality of the image being worked on is any better than on PSE4 - otherwise probably better to pay extra £100 and have the real thing?