This won't be a wide spread thing. In most corporations, people won't want to piss off the boss-man by voting his answer down. Reputation is ego and ego in the work place gets ugly.
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.
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.