While I have been looking over many of the Waves that I can find in public searches, I have been wondering what is the main point of Wave. According to Google, the idea was simply to answer the question: "What would email look like if we set out to invent it today?"
Like I assume many have, I started using it just as the basic interface allows you. Essentially, you get many "blips", one after the other responding to the "blip" immediately above it. It winds up resembling a chat room, where you just happen to be able to edit any existing message.
If you use it as some of the examples indicate, the idea is not that you respond directly to a full blip, but you instead inline responses to individual parts of a blip. The main use case being collaborating on a series of questions or ideas. This would mean that if you had several points in your original email, a respondent could place the responses directly where those points were.
This seems to imply that email is strictly a collaboration tool, when many people use it more for correspondence than they do for collaboration. In fact, I would go so far as to say that it is a major complication to approach Wave like you would an email or a chat. Both of those are just correspondence tools. While it is true that correspondence can be used to collaborate, the best Waves will be like the best collaborations in the real world, where people are actively doing something as well as just communicating. It is only once we learn how to start editing each others contributions that the real value of Wave will be seen.
Wave does not make an ideal correspondence solution right now, maybe it never will. It does look like it will one day make a wonderful collaboration tool, though.