I've been playing a lot of Scrabulous, a Scrabble clone on Facebook, when it occurred to me that a 4X space empire building game could work really well inside Facebook. Think about it.
It would work much better than play-by-email since turns won't get thrown in with all the work, personal, and spam emails. Games would play a quite a bit faster.
Alliances, clans, and play-by-committee games would actually become practical, since the Facebook API gives access to friends lists and there are built in community functions. (If we had a tool like this back in the day, the League of Empires vs Chaos Contingency war might have actually happened.) Plus there would be a central place to find players and open games. Scrabulous lets you invite friends to play or have an open table that anyone can join.
Treaties and interstellar politics would be much more detailed since there's already a built-in messaging and notification system. You could piggyback gifting, trading, and treaty proposals on top of that.
Since Facebook apps tend to spread virally, quick small-scale games could be available to casual players, while large galaxies and quadrants would satisfy those who want their games to last several months or years at a time.
Note: this post is identical to a duscussion thread I posted on the Space Empires Facebook Group.