Warning: This is something of a though-stream, so...

The visible symptom:  
Attracting and retaining people who can positively participate in the community, either both asking and answering questions, or at the least providing substantive answers on some kind of "regular" basis.

This has been an ongoing issue for the site for a long time now. I'm really not sure there is an answer, or where the root of the problem lies. But there are contributing, conflated, and correlated issues.

1. People don't vote. Some people have great voting records, but on the whole SF has less votes per user-views than some other sites in the SE network.

    Contributing factors:

     - Our subject matter is already quite wide, and we may have relatively few experts per subject field. People may not feel comfortable voting on topics they don't fully understand.

     - Many Questions show questionable effort, and many Answers are of questionable value to the OP. It's hard to test potential answers unless you are actually experiencing the same issue as the OP, or have at some point in the past.

    Possibly Related:

     - Questions that have an answer tend not to be reviews by people who may have subject matter knowledge. They tend to be viewed only by new people having the same problem. Many of those new people aren't users, can't vote, etc. At some point in the past some SE sites had a feedback mechanism to allow non-users to indicate a post was helpful - SF doesn't have this, and it didn't affect the post scores anyhow.


    Consequences:

     - We can't rely on voting to blow away bad content. We've established a number of higher-reputation users who can Vote To Close and they patrol the review queue. This leads to a "heavy handed" approach which generally works, but leaves many new users with a negative view of the site. Also, it's extremely uncommon for anyone to leave personalized feedback about what's wrong with the post. New users seem to overwhelmingly ignore the Help Center, sidebar Help, and any other automated help of any kind (perhaps we should just lie to the users and have those messages come from "Joe Blow" or whatever - not crazy about this idea, but I don't have anything better).

     - When people do vote, the reputation of the poster seems to be weighed into their decision (people with high rep tend to accumulate more rep for an otherwise equal post as compared to someone with low rep). This means new users are less likely to receive *magical Internet points*, and less incentivised to be gamed into SF.


2. The majority of our Question come from users who never contribute Answers. These include professional administrator who simply choose not to Answer others' question and users who have no ability to Answer others' questions (ie, [Help Vampires](http://meta.stackexchange.com/q/19665)). We certainly need Questions to keep the site vibrant, but we're tipped to one side.

    For the former group, I really don't know how to inspire people to begin contributing more than the incentives we have already. If anyone has any good ideas I'm sure we're all ears.

    For the latter group, the help vampires... There's a wonderful write on [slash7 with Amy Hoy about Help Vampires](http://slash7.com/2006/12/22/vampires/). What that articles does not include though, is how to deal with those people in mass. The majority of Help Vampires don't realize what they are doing. You can point it out to them, but more commonly than not it takes some significant effort to do so. Worse, it takes more effort on their part to not be a help vampire - and the unwillingness to put effort into their problems is what made them a help vampire in the first place. Regardless, this is all individual effort, see above comment in #1 about people ignoring automated warnings.

    Actually, while I'm thinking about automated warnings - this must be some facet of human psychology. So many disasters have occurred while automated warnings were blaring of impending doom. Chernobyl, Air France 447, Target's CC Hack, and there's zillions more examples where those came from. If anyone has some sort of scientific insight it might be helpful, or at least interesting. 

3. Relatively low signal to noise ratio: SF gets about 100 questions per day on average - about 30% get closed. 51% of questions asked in April 2014 have a score of 0 or less as of writing.

    Contributing factors:

     - See above about drive-by Questioners.

    Possibly Related:

     - Others have pointed out that quite a few questions come from people with some reputation on SO. I'm not aware if anyone has run the data though to see what percentage of closed and downvoted Question from from SO Users.

    Consequences:

     - Sorting through all the "noise" takes effort from people willing to provide Answers. This is effort that could be put into writing actual Answers, but is instead diverted to sorting and filtering.

        To somewhat mitigate this issue, users can setup tag filters. SO has an "Interesting" tab on the front page, which attempts to cull some of the questions you might not be interested in. I think this might help SF, though we don't have the deluge of questions that SO gets (~70x as many as SF). By selecting tags question are highlighted on SF. Though this again necessitates the User setting up these favorite tags, and the Question being accurately tagged to begin with (given that we had to ban a handful of nonsense tags because users try to use them *daily*, accurate tagging is still a problem).

Devs: How about some consistent formatting? WTF with the spacing after a bullet list?