I totally disagree with Crawn2003.
Firstly, you buy a laptop for mobility, why would you bother getting a 17"? What for? If you are a pro photographer, then using the laptop LCD to edit ur photo is a big no no. Bi g LCD 17" for what then if you gonna add in a real LCD 23-30" for color correction?
Secondly, 4GB Ram and 250GB HDD? I would say 2GB RAM is far more than enough. If you want get real fast editing, go for a Mac Pro, not a Macbook Pro. 250GB HDD? Why don't you spend the difference between 250GB and 160GB on a 500GB external HDD with firewire 800?
Regards,
LT
Yeah, you can buy a laptop for mobility but why did they make a 17" in the first place if it isn't mobile? I've had laptops since the Titanium G4 500MHz then went to 17" PowerBook to 17" MacBook Pro and I've never looked back. It isn't that big of a difference (in weight and size) then the 15" MacBook Pros. Really, it just comes down to how you (the original poster) feel about a laptop. Oh, and like it's been said, it's really impressive when you pull out a 17" MacBook Pro in front of a client. It gives them the feeling that you have money/business to afford the larger laptop and, well, it just looks cool!
As for the additional LCD, yeah, you have to add it on the side but if you're getting a laptop and plan on doing color correction anyways, it's a necessary evil. Otherwise I'd say get a iMac or Mac Pro instead of a laptop but you're sacrificing mobility. Either way, an additional screen is needed if you get a MacBook Pro just for color correction. That doesn't mean you need the 30" Apple Cinema Display. A 20" LCD along with the MacBook Pro is an ideal setup for that computer.
I have to disagree with Libertyterran, 2GB just won't cut it. Really. It'll get you by, yes. Will you be able to run Photoshop, Capture One Pro, Aperture, etc. at one time - yes - but it will be a little (maybe a lot!) sluggish. Trust me, I've found over the last 6 years that the more memory you have, the happier life gets. I find that OS X is snappier, that programs just run smoother with more memory, and life is less frustrating. Also I found that I don't have to worry as much about pageouts that occur in OS X. A pageout is where OS X uses the hard drive as additional memory when there is not enough physical RAM available.
Also another thing I disagree on with Libertyterran is the HD at 160GB. Yeah, there is a price difference but let me put it to you this way:
Life can be a cluttered mess. When you're at a clients do you really want to have a external drive in addition to a possible mouse (if you don't like the trackpad) and power cord? (sometimes happens but I try to show up with a fully charged battery just for the sake of not having another cord)
I would never show up to a clients place and have to stop and plug in an external drive. That just looks cluttered to me. I like having their work right on my desktop so that I open the MacBook, open their folder, and there is the shot. There's no lag with having to get out an additional drive, plug it in, wait around 2 seconds for it to load onto the desktop, then find their file to open. That takes too much time away from the client, and as you may know in the professional photography world, it's all about time. If you, photographer A can get the job done faster and more efficient than photographer B, you make more money and get their business again later. Also this gives the client a personal feel, like you have their shots right there for them and not filed away somewhere else.
Really, it all comes down to what you want. I can only give you my real world examples and how I feel as another professional photographer.
Good luck and hope I helped/clarified everything. If something doesn't make sense about what I wrote, post back!
~Crawn