There's a band called Kneebody that has taken this idea to a new level:
http://www.youtube.com/watch?v=X42GIjWz1z0
They have an extensive vocabulary of musical cues, riffs that indicate to the other members "I'm going to change key now" or "I'm going to change time signature now".
For example, after playing the "I'm going to change tempo now" riff, a musician will play four quarter notes at the new tempo, and the rest of the band spontaneously adjusts their parts to the new tempo. They can pull this off because they've been playing together for years.