I saw a production of "Anything Goes" with a cast of 60. The choreographer was brilliant. She put all the dancers in front and had everyone else doing choreographed movement with an occasional tap all together. It truely looked like she had taught all 60 members of the cast to tap. I was impressed with her ingenuity. When I spoke with her later she said that she had broken the cast into groups based on experience and ability. She then choreographed to each group working the whole thing into a big number. It made all the dance numbers impressive and enjoyable for everyone on stage and off.

There are a lot of great comments here. I just wanted to add that even when utilizing professional dancers, great choreographers like Fosse, Robbins, and even Susan Stroman show their genius with the simple things, the little movements, the gestures that define a character. Anyone can throw some virtuosic steps at a well-trained performer and have them look like dynamite. But the things that most often blow my mind when watching the masters of choreography are the "simple" things.

P.S. Did everyone see that dance has it's own forum? Yay!