There was a podcast a while back that Leo Laporte participates in that discussed purchasing a Macbook with a caller. Here's the gist of the recommendation and I agree with it for the most part.
So should one get a Macbook or a MBP?
Generally speaking, get a Macbook. Here's why. You can buy one and cram 4GB of RAM in it as well as a 250GB HD and have a machine that is just as functional and powerful as a MBP. Plus it comes in a more durable case. The MBP has a metallic case that may scratch, dent, and ding easier than the Macbook enclosure. Now, there are a few points in favor of the MBP. The screen size is considerably larger. The Macbook has about a 13 inch screen and the MBP comes in 15 and 17, so you get more real estate. The MBP also has a better graphics card. The MBP also has a 300GB HD as an option. There are some other differences with regards to ports availble on each, but the overall picture for the average user is the same.
Like any computer, it all depends on what you want to do with it.