Don't fall into the same trap I did. When I was looking to buy PS CS3 I noticed that for a little more $ I could get the Design Premium collection that would not only give me PS but also several other titles that I thought I might use someday. While it's not Adobe's fault that I have never used any of the software other than PS, now that I would like to upgrade my PS to CS4 I find out that the only way to do that is to upgrade the entire collection which costs about the same as a full version of PS.
So the bottom line is that by spending more money and buying the extra software I am being penalized at upgrade time. I am unable to buy what I want and instead am forced to upgrade stuff
I don't even use. My choice however is to not send Adobe another dollar until I absolutely have to.
No upgrade, I'll live with PS CS3 as long as I can and I will never buy another "collection".