I actually use it though. I brew beer, and I use it to store and share my beer brewing recipes. It has the property of being both a document that I can edit and a record of when I brewed the beer. There are no plugins supporting this yet, but I want to write some that do calculations within the wave. There are currently better apps for beer recipes (Beersmith, BeerAlchemy, etc) but I can imagine free Wave plugins taking over that space.
So what is it -- why do people think Wave is irrelevant? Do they have no imagination for how Wave could start to dominate collaboration with a few cheap-to-develop apps? Was Wave excessively hyped before it developed the features needed to support the needs of the masses?