This demonstration video is pretty long but it's really cool.
It's funny because I've felt the need for an application like this lots of times. When I am planning a trip with another person, say to Thailand for example, we are both doing lot's of research and trying to find the best places at the best prices. Then we have to dump links into email and hope the other person reads them or likes them and just wait for a response. Then after an amazing adventure, we'll have pictures on several different devices that we want to share quickly. These little snags are compounded when your travel group is four or five people. Google Wave sounds like it will make this process smooth like butter.
Now the question is, who is going to be a pal and give me an invite to Google Wave?