I use a 15" screen to edit photos and have no problem, but I also don't see why it would be difficult to work with the 17" screen. When you're working with a photo editing program it doesn't matter what format your screen is in (wide or normal aspect).
I've heard mixed opinions on the glossy screens. Some people say that they're difficult to work with because of the reflection. Personally I think I'd agree (but I don't have a glossy screen on my laptop so I can't really compare).
I'd say the most important things that you'll want to consider when finding a laptop are:
- Hard drive space: You're editing pictures, you need lots of space, it's a given
- Memory (RAM: Photoshop can be a memory hog. If you do any intense processing, you'll need a decent amount of memory (then again, I think most laptops come with at least 1GB now)
- Possibly a video card that does not have shared memory. Nvidia is always good.
Those would be my main considerations, but you may also want to consider what else you would use it for when you're deciding on your final criteria
