Well my understanding is that you can do this but it will charge your MBP a lot slower than it would normally (same as the way the iBook chargers charge PowerBooks incredibly slowly. It still might be worth it for the smaller size if you don't need the battery that much. Then again if you need it portable you probably need the battery 🙂
I wouldn't recommend it. I have no idea if it would cause any damage but using an ibook charger on my PowerBook never seemed to do any harm.