Go for a Mac. I've got a feeling new iMacs will be announced on August 7th, according to a few rumour websites so it might be worth holding out, also they will be dropping the 17" so personally I wouldnt go for one. To be honest Photoshop isnt that graphics card intensive, so you should be ok with the MacBook, it all depends if you want to be portable or not. I think one of the best thing's I've ever done was to buy my MacBook Pro, I've got an iMac too, but my MBP is so powerful I can use it as a desktop by plugging in a keyboard and mouse and external monitor if I want (like Nick Carter) or I can have it on my lap and still work just as well. Like you said, there isn't much difference between the machines technically, the MacBook has slightly slower RAM, smaller hard drive, a CD writer (not DVD like the iMac) and a less powerful graphics card, but my sister has never had any problems with hers. At the end of the day it's up to you, but I'd say currently go for a MacBook, or if you want the iMac, wait until mid-august.