I will be the dissenting opinion here. Wait a year, and I think that Wave will be mostly complete (but not necessarily out of beta :-) and generally useful. Being able to embed Waves for discusion lists, etc. on plain old web sites and have Google provide the persistence on their servers may be a 'killer feature' of Wave.

I was at a friend's house for brunch today and mentioned the embedded Wave feature to another non-technical friend who has a very plain web site - this would be perfect for people like him: no change required in using cheap hosting.

Wave is also yet another platform for developers of web services (via Wave Robots), and I think that this will be another 'killer feature.'