An i7 processor with 4GB of RAM is a waste (IMHO). If you get that processor, go with at least 8GB of RAM. It'll take 16, but that can get pricey. If going to 8GB puts it out of your budget, consider adding RAM later, which can often be much cheaper. Crucial is a great place to buy RAM and adding RAM to a MBP is a snap.

The screen on the 13" MBP is incredible. I'm not sure how much Photoshop work you do, but the 13" screen on that is surprisingly roomy and very vivid. When my Dell Z600 finally goes, I'll be looking at a 13" MBP to replace it.

As far as the switch to Mac OSx, I don't know. I've played around with it and it seems easy enough, but I'm too used to working with Windows. You can run Windows7 on a MBP chassis by using Bootcamp. You'll need a Windows7 license, of course.