You can have a look on a nice video over Google's new project here:

Wave

I don't know what to think of it yet, seems nice but I have to lay my hands on it to have an opinion about if it has a purpose at all in the first place.

From a technical standpoint however, it is pretty impressive. Huge huge "Holy Sh!t!" factor in there. It is really impressive to see what they can do in HTML and JS (and gears for the drag'n drop feature).

I can't wait to test this. If it is half as good as it looks, it's gonna be HUGE.