I'm a recent Mac convert... I'm using a 15" MacBook Pro with the Core i5 CPU at 2.4Ghz. (the additional cash for the i7 CPU just isn't worth it IMO). I did switch out the stock 320GB 5400KRPM hard drive with a Seagate MomentusXT 500GB 7200GB drive (the Segate also has a 4GB SSD that really speeds up performance with commonly used files) and upgraded to 8GB of RAM (purchased aftermarket through OWC, cheaper than buying through Apple). The MBP isn't going to be my main editing machine, I'm about to order one of the brand new Mac Pro desktops, the hex core 3.3Ghz model but I still wanted something that could handle a good bit of CPU/memory intensive work on the go.
I use Lightroom 3 and Adobe Creative Studio 5 and both run quite well chewing up my Canon 5DMkII RAW files (I can shoot over 40-50GB of images in a single day, and it eats them up without issue) and can even do so while running VMWare Fusion with Windows 7 Ultimate running in the background. I shoot tethered into my laptop sometimes and I've had no issues.
A few things I'd tell you:
1.) Don't order the 'upgrades' from Apple unless you don't have a choice... If you want to upgrade your memory or hard drive do it aftermarket.
2.) The Apple provided 7200K RPM drive sucks compared to the other available options, and in fact I've seen some folks point to the 5400K RPM drive from Apple performing almost as well. So if you want a 7200K RPM drive definitely buy it aftermarket.
3.) If you want to drive a 30" display I think you need the video card with the 512MB of video memory.
4.) Consider reading through the Mac Performance Guide, the guy brings up a lot of great things to think about. He explains things in a 'max performance no matter what' manner, which is good one just needs to understand that not everyone needs max performance and in some cases you might be spending hundreds or even thousands more to eek out just another 10-20% more performance (which most folks don't really need).
5.) Take peoples advice with a large grain of salt... There is so much mis-information online, specifically in web forums like this where lots of folks aren't professional photographers and in most cases aren't IT professionals. I guess all I'm saying is try to read from a variety of sources and try to understand for yourself as much as you can and know that some information might sound solid but just isn't. Even take my advice with a large grain of salt and weigh it against what else you read/hear from others.
... that said I'm a pretty big geek who has spent almost two decades designing server systems architecture for large and mid-size companies (including one where I had to integrated 50 Mac clients into Windows Active Directory), and has spent the last four years shooting on a professional basis on the side from my day job.