There's something to be said for the extra screen space afforded by the Macbook Pro over the Macbook. Whether it's worth it depends on how you use your computer.
That's true, but that's what monitors are for. The times when you can't easily have a large external monitor are precisely the times when you don't want a big, unweildy laptop. I find the Macbook screen is a nice balance.
What's the max display resolution a MacBook can handle when plugged into an external monitor?
It's 1920 x 1200, just enough for a 23" Cinema HD.
When I spend an extended amount of time hacking on my Macbook, I find myself missing the extra resolution. The width is fine, but the height is just lacking. Whether or not that's important is probably a personal preference, but I know I wish I had gone with the pro, just to get a handful of extra lines vertically.