For teams working on projects within an organization I can see this being a killer app. Keeping the documents together with the discussion of those documents is useful (I know other office type apps attempt this, but more as a hack bolted onto a word processor or something, as opposed to part of the original design as it is in Google Wave)
The question will really be adoption. Which, I imagine, is part of the reason Google is open sourcing it. If it becomes something that people find useful in a business environment, then it'll become common enough that it'll get used at home as well.
And although the 40+ crowd will likely have problems getting used to it, the upcoming generation who grew up with email, IM, online photos, facebook, etc... won't have a hard time adapting to this.