I started using Photoshop with CS, shortly after CS2 was released and i grabbed it. Then i got CS3 at BETA stage and i haven't looked back since. Albeit most of the work flow is pretty similar between CS2 and CS3 i find it much easier to work with the layout is much neater and user friendly allowing you to order pallets etc. Extended ofcorse also has a few extras over CS3 but unless you need them theres no need.
I currently work with CS3 Extended (Win) at home and CS3 (Mac) and CS (Win) at college. I would easily take CS3 or CS2 over CS, it has a few extra little shortcuts i know off by heart that don't exist in CS and much faster ways of doing things, like being to select multiple layers at once.
I also briefly used PS 7... Lets not go there