I found wave useful too.....well, would have.....
....if it had worked properly and been more flexible. As a unified method of dealing with interactive collaboration it is quite spectacular. Being able to combine different media and to record the development of a wave and replay it has a number of applications for which a solution currently does not exist in the real world.
Imagine a bulletin/message board with waves for threads/topics. Subsequent contributors can add/amend/insert material in the relevant place, without having to quote previous posts and append it at the end. It could be mixed media...and anyone joining the discussion could play the thread to catch up. Of course to be able to do that it needed to be able to be hosted on ones own servers/hosting, to be integrated into a wrapper that is site specific, and to allow a diverse range of enhanced admin options (for example privileges for read/write/edit of existing waves and to be able to control who can publish new waves).
....but now think that you can use the same mechanism for private messages, public messages to people unregistered at the site, you can also use it as a collaboration environment for writing white papers or as a project management tool. Think of it as rtf for the internet age.
Google indicated that this would be possible, and tried to get developers on board to work towards such integration. Why didn't it happen? Well it partly did, it's just that the technology is immature, the feature set outside the google hosted wave servers substandard, and the google hosted waves lacked the community (of either developers or users) to gain momentum.
Wave isn't a fail, though. Get the technology right, integrate it into specific applications, and distribute freely in a truly non-proprietary way, and I still believe it's a game changer.
The question is, who pays?
It's an Apple Newton moment. Absolutely brilliant idea, but fundamentally unusable in its current form. Look forward ten years, and the showcased concepts behind it will be ubiquitous.