What about vendors/developers answering questions about their own products?  There are a lot of free/community edition products discussed on SF, with users asking for help.  Should support reps or developers from these companies be allowed to answer questions?  (It was suggested on another posting that no).

You can argue YES since they are adding to the body of knowledge to serve (professional or not) administrators, or you can argue NO since SF is not "internet tech support".  That really gets to the point of the question...

I think the purpose of SF is to build a detailed body of knowledge on admin tools/sw.  Who should use it?  Who cares.  Who should be allowed to contribute?  Who cares.  There will be a wide range of questioners and responders...so long as they all benefit from the same body of knowledge that's all that matters.