I played Scramble on Facebook for ages before they brought in the policy that all third party apps must support SSL and Zynga decided, for some reason, that they didn't want to (or couldn't) with Scramble. It was basically Boggle: the only obvious difference was that scoring didn't eliminate words which someone else got (because that doesn't scale well beyond four or five players - almost everyone ends up scoring 0). It's possible that the dice were different as well, but who knows?
The basic rules of thumb are:
- Game mechanics don't fit into any of the categories of IP. While the text of the rules can possibly be copyright-protected, the way the game plays can't.
- Game images and non-functional design can be IP.
- Trademarks are definitely IP, and some companies are very aggressive about what they consider an infringement on their trademarks.