I get nervous doing that - most of my database design is from reading one book many, many moons ago and then a lot of work.

I think auto-increment keys like that are cleaner. By using a database, you have kind of already said you are not *that* concerned with size. An extra INT between friends shouldn't matter. And composite keys, especially when referring to foreign keys, just sound very dangerous to me.

But I have no theory to back any of this up - it is your database to design as you wish.
Mik