Pain in the rear to count out the m&ms total) but everyone loved it so I would suggest it at any shower. When they are passing the bottle around to guess is a great time for people to introduce themselves.
I always do this game with some kind of candy. gumballs, m&ms, jelly beans. For baby showers I like the idea of games and activities around the room that people can do of they want, but not many forced group games. Baby shower games by