I understand that questions on AC.SE are going to be "softer" in nature than the programming questions typical of SO.SE, but I think our answers often are "softer" then needed. I often read answers and think "Citation Needed". Are we answering questions based on our personal experience when we could be providing answers based on well conducted research? Should we be up voting "easy" answers that we agree with when they are void of references?
This is a very difficult area for our forum, as most of the answers and advice dispensed here is not borne of thoroughly research, but rather real-life (and therefore pretty localized) battle scars.
Personally, I favor the "hands-off" approach; policing this sort of thing is very tedious, with minimal benefit, as the community tends to do a good job upvoting stronger answers over the soft ones. As the distinction between strong and soft answers is typically pretty nebulous, I don't think a policy-based approach for treating this is correct. If this is something which needs to be addressed (which I'm not sure of myself), I would much prefer an education-based approach. One method could involve a community-defined comment template to leave on those sorts of answers, suggesting the commenter leave stronger answers and directing the answerer to the appropriate meta discussions. Another parallel method could be to make use of the community blog feature to publicize posting guidelines and suggestions. I would much prefer these to policy.
I think that, without forbidding experience-based answers and anecdotal evidence, we should push ourselves a little harder towards fact-based and statistics-based answers. There are quite a few questions on the site who are answered mostly with “I advise you to do this” or “I observed around me that X is more common than Y”, and which could be much improved if they were backed up with links to actual official policies and/or statistics.
Now, how to do that? I myself try, on questions where it is appropriate, to add a comment to try and remind us that fact-based answers are at the core of the Stack Exchange Q&A concept, and while we have a “softer” policy than most other sites of the network, fact-based answers are good. While I don't always add such comments (also because I don't want to cast myself into “that guy”), I think it's overall a great strategy to steer us in that direction, without policing. So, please consider adding them too!
I agree with eykanal, and also prefer an "hands-off" approach. We already have mechanisms for dealing with "undocumented" soft answers: down-votes, comments and even deletion. In extreme cases, there is even a mod mechanism allowing us to put a post notice indicating that a post requires some citations or some further explanations.