Obligatory response to this (and most) web startups: why won't Wave kill this?
Look at Twitter and say: "why won't blogging kill this?" Part of the answer is focus: they're making some things easy, not just possible.
Part of the answer is demographic/cultural. Reddit isn't Hacker News, even if a lot of the technology is very similar, and StackOverflow isn't any of its many different-topic clones even if nearly all of the technology is shared. A community is affected by focus, policies and advertising, not just the technology.
If Google Wave has the technology to kill most web startups (I'm not sure I believe this), then it's not focused enough to matter in almost any of their specific domains.
It seems like this is exactly what Wave is designed for.
Half of the point of my original comment, however, is to say that Wave seems to be designed exactly for everything, which is one of my biggest criticisms of it.
From their Site..So i believe this gives a more personalized experience for the user and their family. I am not saying this app will be a killer app right away...But i can definitely say Wave Wont kill this...