philipma1957 - thank you very much for your insight and your thorough response.
I'm actually coming over from the PC for the first time -- and while I do 80% of my work on my laptop, I'm planning on using the mini 2.0 QC i7 for light cs 5.5 (dw, fw, ps) with no files over 500MB -- basic web development stuff. I already have 2 x Dell u2211h's that I love, so I don't want to go with an iMac (though I do understand that the iMac has more power and can take 16GB of RAM at a much more reasonable cost) or a Mac Pro (price point is too high).
My concern is that while I'm looking to go to the mac, I will still need to run office and cs5.5 through parallels/boot camp for the time being. If I'm happy and productive on the mac platform (believe me, I'm scared) then I will replace my pc laptop for a MBP and then go native mac on CS5.5 and office.
It's just that I don't want to make the leap with new software before I know I'm happy (and as an aside Adobe's open licensing will allow me to have mac and pc copies of CS.5 -- but I can only run one platform at a time hence the need for a Windows 7 VM).
Which brings me full circle back to the hard drive question. I now believe that 8GB of RAM is fine for what I do with CS 5., but I'm worried that with 4GB allotted for parallels/win 7 and 4GB for OS X, I may be cutting it close. Thus, any advantage I can get with HDD speed is one I'd want to take. (And I'm not interested in SSD right now as I'm planning on running lion of HDD1, and boot camp on HDD2 [and thanks to this forum for that and a lot of other advice]).
And thank you for the RAM recommendation and all of your input.
R