I've upgraded my photoshop since Ver 5.
The big difference fo me in 7 - CS(8) was things like the filter browser. It's handy.
The interface and layer options have some enhancements.
Admtedly there isn't a giant leap but 8 is very good and stable. I like File Browser. Its really useful fast and responsive.
CS2 sucks ass. They ruined photoshop, it seems to have memory holes, is sluggish.
With both 7 & CS I hardly ever saw the spinning wheel of death, even when a project amassed a large number of layers.
With CS2 it stops up on you and SPOD is seen very often, even when selecting somthing fairly simple like a text layer.
After paying for the upgrade from CS - CS2 I feel really pis*ed off at Adobe. Even fantastic FileBrowser from CS has been replaced with Adobe Bridge 1. An extremely slow and labourious program. The benefit of file browser was its speed, take that away and over complicate somthing unecessarily and hey presto you have Bridge.
Also Version Cue sucks ass, its like spyware attaching itself to the top menu bar and monitoring you. What a waste of resources.
7 - 8 worth it. 7 or 8(CS) to 9(CS2) CRAP.