Positives: As far as collaborative communication is concerned, Google Wave really is impressive. We recently started a LUG (Linux Users Group) wave, and I think we've done more constructive communication on that wave in a couple days than we have done in the last six months on the mailing list. Widgets are fun. I wish there were more of them. Real time communication is a good feature. Waves can be read across platforms (Windows, Linux, Mac, Handhelds. etc.) Negatives: Lag can be an issue, especially during real-time communication. Sometimes, clicking to reply (or clicking several times while waiting for the window to open) will cause multiple reply threads to open, which can be annoying to delete. More widgets would be nice. I assume that that will increase over time. I interacted with Wave on a Palm Pre emulator, and although I was able to load Wave and read waves, my ability to interact with those waves was less successful, since wave employs a fair bit of right clicking, holding and dragging in its interface, and I haven't quite figured out how to do those things in my Pre emulator.
Wave is a tool that I plan to continue using. It could be a tool that changes the way that people communicate, both in work and outside of it. The edges are still pretty rough, but I expect that Google will continue to polish it into a fine program.