I've had my MBP for a couple weeks now and I love it. I got the upper 15" one with an upgraded (160 GB) hard drive. If you are taking RAW photos, hard drive space fills up dramatically fast.
I'm an enthusiast when it comes to photography, and I just tried Aperture on my friend's MBP today and it is an amazing program. I'm sure it becomes even more so when you learn as much as you can about it. I have not tried lightroom yet from Adobe. Luckily both are available as a free demo.
The only other thing I can think of is if you need the 17" as opposed to the 15". I was using a 12" iBook before this so the 15" feels like a monster of a screen, but I know to some it isn't big enough.