And I'm not alone. The game has spawned guides, a wiki, and according to this piece by Dean Takahashi, the company that runs Warbook has garnered a billion page views in 90 days. The game's Wikipedia page claims 140,000 active users, and 750,000 total players. That's big time.
The game itself has a little ways to go-- the core gameplay consists of amassing gold in real-time, and using it to build up your kingdom or army, which you can then use to attack other players for a simple XP system. It's your (very) basic empire building game with a few RPG elements thrown in, except that the fact that it's integrated into Facebook turns it into a very massive and persistent multiplayer world. Fascinating stuff. Warbook is just the beginning of something much bigger (basically, the creators are leveraging popular social networks directly into casual MMO gaming), and it will definitely be fun to see what this means for the MMO industry at large.