Rationale for going to a MacBook from a Pro is this:
I spend 95 percent of my time with an external monitor. A 24-inch display at work and a 30 inch monitor at home. The two extra inches of built in display, while nice, aren't necessary if the normal MacBook can drive a 30-inch display. The size and weight reduction are a nice bonus.
The majority of time I am without an external display is late at night checking emails from bed or the couch and on airplane trips. Both of these occasions, I would rather have a 13 inch display. Even when presenting on a projector, I am happy on a 13.
I am not a big gamer and I don't do any 3D apps so the integrated video is more than enough for my mild Adobe CS4 dabbling. I don't need the 9600 chip that the Pro has.
Also, the economy isn't doing terribly well (as you might have heard), so I thought it'd be prudent to cut my employer a break instead of knee jerk requesting the most expensive laptop Apple makes (like I normally do).
I got the new base aluminum MacBook model with 4Gb of RAM. Normally, I get 3rd party RAM but Apple has lowered its memory prices to within reason ($140 extra) and it is part of the Apple warranty so a few extra bucks is worth it. 8GB would be nice but not cost effective.
Lighted keys are cool but not necessary for me. The base model is not lit. Your mileage may vary.
I opted for the base 160Gb drive because most of my media is on a media server at home and my work files are available from anywhere via VPN. I know it is easy and inexpensive to upgrade the hard drive in a year or so if I feel I need to. The new case design means the upgrade process takes about a minute.
I use my jailbroken iPhone with PdaNet for 3G access which works as well as any Bluetooth/ExpressCard 3G modem I've ever used. It would have been nice of Apple to include 3G and WiMAX but they think I am nuts to want this.