So I woke up one morning and decided I don't like Gavin's and Jeff's bitcoin clients for any of the platforms.

Can I write my own, and is there anything technically stopping me from doing this if I were to follow the rules of trading/transactions on the Bitcoin network?

Maybe I want to write a Haskell or a Clojure client... or Ruby. Is there anything stopping me from writing one and getting other people to use it if they see value in it?

Where is the protocol specified of how to write a Bitcoin client/daemon?

Thanks!