It's not very easy to do with PBP due to all variables being global and the lack of proper function calls where you can pass parameters.

Just one very basic example:
Say I write a "library" for a GP2Y0A21 distance sensor and I decide to create a variable called Distance. Then you create a "library" for driving a motor with encoder feedback and you decide to create variable called Distance. Then comes the "user" and finds our, on their own, great "libraries" and wants to use them on his/her new robot. Well, you know what happens.

/Henrik.