Upgraded CS3 to CS5 ... one of the things I like about 5 (that 3 didn't have) is the ability to drag windows and arrange them as tabs. Still tinkering with it, though.
I didn't have CS4, so I wouldn't know hehe. It's slower a bit than CS3 (or maybe it's just my computer) ... but so far, I like the changes.
lol i want it free.... I'll probably pay for cs5.... I don't have any photoshop besides free programs but have done over 30hrs+ doing tuts and crap in my class that im taking in cs4... I think cs4 works great but wanna try cs5