I'm somewhat surprised that Google doesn't offer something like this already. They have more resources than Stack Overflow and organizing information is supposed to be their forte.
Overall, though, I would have liked to see a Stack Overflow inside some of the larger organizations I've worked at.
We're actually pushing into the corporate space with ErrorHelp-- but there's a lot less ego involved there (everyone runs into random unknown errors, really). Answers grow passively rather than being something people have to read each day to provide answers.
I work for a large (65000+ employees) telco company, and our in-house problem/solution reporting database is totally broken. The search function is crap (it's based on predefined keywords, not really on free text). It has a voting system, but the votes are not used to classify the quality of the problems/answers. They are only used to track how active an engineer is browsing the database. You can randomly select problems and write nonsense commnents, the net effect is the same.
With a corporate Stack Overflow there would be no employee/boss conflict, since in my company all the users on a given domain are at the same hierarchy level.
When I discovered Stack Overflow I inmediately thought how good this would be to replace our corporate tool.
Story/tasks wouldn't decay with time, but only by being (1) finished; or (2) deprioritized with regard to others. Karma could be two-sided: points for proposing the right things, and (even more) points for actually implementing them.
(There'd be ways to estimate effort; split oversized items; claim/merge items to avoid redundancies; calculate community 'velocity' over time; etc.)
A few anchor project/community managers might have admin powers to pin certain overriding goals at top, or 'dead' digressions, or change the relative payoffs for proposing vs. doing, etc.
That is, what if a community much like HN compulsively hit 'reload' and earned karma not around ephemeral (often attention-abusing) 'news', but instead around incremental goals on a shared project?
Add the answer component and that would be it, no?
If I had my way, we'd throw away the current GWT implementation for a version that used unobtrusive JS and was a good netizen. Of course, if I had my way all the time, I'd also have a pony.