CS3 is out now, runs pretty smooth (ive only found one bug with it, and its not major).
Its possibly worth upgrading, but it depends if what you already have meets your needs.
If it already meets your needs perfectly, id stick with it. I only went to CS3 because my camera take photos in RAW 4.0 format and CS2 only supports upto RAW 3.7 format.
There isnt a great deal of difference in speed between CS2 and CS3, not sure about PS7 and CS3 though.