Google Wave is a new communication medium by google that sits somewhere between instant chat, a forum and collaborative website. It's very difficult to explain but it is cool to use.
The benefits to roleplay is that it can be both instantaneous and played back over time. I think that is important because you can have the action move along very quickly and players who have missed a few days can catch up easily and in the right context.
You can also add gadgets to a wave that do dice rolling and the like for everyone to see. If you are playing a modern game, you can use Google maps. It's brilliant for that.
I must admit that I am more tempted to run a game like this than on Skype, PBP or elsewhere. Especially, if you and make use of the resources .
I am not offering to run one just yet but want to discuss it as a concept. Have you been involved in a Wave RPG game? If so, please tell us about it. What worked, what didn't? How did you deal with player absence?