The only thing that would stop me from getting a MB over a MBP is the screen. The "new" MBP LED-backlit screens are amazing!. So clear and bright. The MB glossy screens definitely leave something to be desired. They aren't terrible by any means, but in comparison they just suck. If they fix the MB screens then its basically a no brainer. Put 4GB of ram in the thing and be done with it.
I'm running an old 1stgen alu-Powerbook. It works well enough that I can't possibly justify buying a new one. I'll probably get the Macbook as its pretty cheap when you get the entry level one (especially with the student discount, which I am). I'll surely put 4GB of ram in it though. With that $1000 I save on the macbook pro, I can get 2 months rent, 2 months groceries, a track bike + 1 month rent, a nearly complete climbing kit, a new surfboard and a track bike. I guess you should look at what You'd spend that $1000 on. If you'd spend it on really great things, get the macbook. If not, get the macbook pro for its wonderful screen and fasterness.
The missing LED screen is the only thing that keeps me from buying a new macbook today. I am sure apple is going to streamline its production and sooner or later also the macbooks will come with a LED backlit screen. The air already has the 13 inch screen. So its only a tiny step until also the macbooks get it.
I have a MBP and leave it on my lap all the time. It does get warm, but never uncomfortable. If you are just surfing the web, working in textmate, running a webserver and/or a db it will stay pretty cool. If you decide to play some games or render some movies you should probably find a desk for best results.
My 1st generation MacBook Pro was definitely too hot to use on one's lap. But, I've seen reviews that said the 2nd generation one ran a lot cooler (due to the 65nm Merym Intel chip), and now the latest generation is said to run even cooler than that, due to the cooler, 45nm Penryn chip.
Also, it's worth noting that all of Apple's laptops run extremely cool to the touch when the fans are running. If it's an issue for you, you can download smcFanControl (http://www.macupdate.com/info.php/id/23049) and manually turn up your fan speed a bit. This will make even the MBPro _cold_ to the touch.
Off topic a bit, but conversely, I opened up my MBP and reapplied the thermal paste on the processors. It was a mess when I first opened it up, and that was causing the heatsink to not accurately pick up temperatures, ultimately causing the fans to never turn on. I was hesitant to use a software solution when it was a hardware issue.
Then again, it was risky because if the MBP didn't boot after I reapplied the thermal paste, I would have a very expensive paper weight on my hands!
Add 4gb ram and firewire raid: developers dream.
It's got everything you want.
It's more durable than the MBP, but the number one reason the MB beats out the MBP? It won't toast your lap.