[lazerwalker]

Smule's launch-era iPad piano app (maybe it was called 'Magic Piano'?) had a similar feature, but it was only you and one other anonymous person. I thought that was a lot more effective, since if the two of you could figure out how to coordinate without speaking/chatting you could have a really fantastic jam; the massive number of people on this makes it hard to create anything that doesn't resemble complete cacophony.