When you factor in the cost of 4GB of RAM, it's only about £80-90 more. Having said that, some people prefer the polycarbonate look, or the trackpad feel.
Precisely, for me the issues are:
The Poly-carbonate look, I could Save money, the Track pad feel (personally the MBp repulses me to the bone), I can type almost without looking at the keys so no need for the Back light, auto dim can be annoying, no need for the better screen, the glass screen is an issue, and, I have no need the firewire or the SD card slot.
Simple.
I could buy plenty of things with the £50 that I would have saved, and even more if I used Educational discount. With that I could buy a selection of these: The extra RAM, a Card Reader, a Mini DIV, keyboard, and mighty mouse. I think that makes it worth while.
To be honest, in my position you are paying for the name. And I would not want to use the Track pad or have a glass screen. I would hate to have to pay £50 to have a faster machine, but one that has things I dont need, and is annoying to use (track pad and glass screen).
There is another thing. No one, who isnt a Mac geek, will care that you have a Pro. The white is classic for mac, and I like it for all its down sides. However looking at the MBp, It would be nice to have the aluminum shell, that would be nice. But that's it, for me its a no brainier. But it is just personal preference, and in no way an obvious choice. They are essentially very different machines for very different people, just with almost the same specs.