user948: Can the community (or a select* portion thereof) vote to ban a user, or can a moderator exercise that power independently? Should this be possible? What would be the grounds, and how extensive (just username, by IP, etc.) is it? Is there some sort of warning/probation/disciplinary process first? From a personal perspective it seems like there are some users who just don't add to the quality or reputation of the site, and I don't really know how to approach it, other than by trying to ignore them.
* how would this be determined?

user69: As community moderators we do have the ability to place users in timed suspension (sin bin/penalty box) for a number of reasons, including but not limited to:

Persistent Low Quality Questions
Repeatedly asking the same question
Voting irregularities 
"Revenge Downvoting"
Being abusive to members of the community
Vandalising own content
Excessive promotion of another site or third party venture
Plagiarism

Built into this system is a facility for issuing formal warnings before a suspension which is always a last resort and is always temporary (though in vary rare cases suspensions can be very long).  This system has been used in the past on Biology.  Further rationale for introducing the system is described in the blog post announcing it.  It should also be noted that there is talk between sites on the network and in some cases network wide timed suspensions have been issued where there is problematic behaviour on multiple sties. The timed suspension state locks an account to 1 reputation for the duration of the penalty, allowing the user only the ability to read from the site rather than contribute to it.   
As for action the community can take, it is limited (rightly so) to confidential means (i.e. flags) between users, moderators and Stack Exchange employees.  If you are particularly concerned by a users behaviour then raise a flag on one of their posts explaining the wider situation.  
Alternatively if there is a particular piece of content that is offensive then you can cast an "Offensive Flag" on it.  I'll admit this is hidden away in the flag dialogue, but is under Flag -> It is not welcome in our community:

This question contains content that a reasonable person would consider offensive, abusive, or hate speech.

If 6 community members (or one moderator) raises an offensive flag on a post then it is deleted and the poster 'fined' 100 reputation points.  This is not an insignificant penalty, therefore please take care to read the description of the flag before raising it or it will likely be declined.  Further information on the offensive flag can be found on the central Meta Stack Overflow.  Flags on comments work slightly differently (and without the reputation penalty).
Another option (again only available to community moderators) is to place the post that is causing issues into a (usually temporary) 'locked' state where no actions at all can be taken on it.  This in theory allows all parties to take a step back and cool down from a situation, indeed it was used on the question you linked to.  
Finally, for those posts (posts, not users!) that you don't think are adding to the quality of the site you always have your downvote available to you to express your opinion. 

I hope that the above is a fair summary of the options we have at our disposal, and I hope it helps answer your question. However, I also hope we have little cause to use them in the future as they are never decisions taken lightly.     

948: <p>Can the community (or a select* portion thereof) vote to ban a user, or can a moderator exercise that power independently? Should this be possible? What would be the grounds, and how extensive (just username, by IP, etc.) is it? Is there some sort of warning/probation/disciplinary process first? From a personal perspective it seems like there are some users who just don't add to the quality or reputation of the site, and I don't really know how to approach it, other than by trying to ignore them.</p>

<p>* how would this be determined?</p>
 69: <p>As community moderators we do have the ability to place users in timed suspension (sin bin/penalty box) for a number of reasons, including but not limited to:</p>

<ul>
<li>Persistent Low Quality Questions</li>
<li>Repeatedly asking the same question</li>
<li>Voting irregularities </li>
<li>"Revenge Downvoting"</li>
<li>Being abusive to members of the community</li>
<li>Vandalising own content</li>
<li>Excessive promotion of another site or third party venture</li>
<li>Plagiarism</li>
</ul>

<p>Built into this system is a facility for issuing formal warnings before a suspension which is <strong>always</strong> a last resort and is always temporary (though in vary rare cases suspensions can be very long).  This system <em>has</em> been used in the past on Biology.  Further rationale for introducing the system is described in <a href="http://blog.stackoverflow.com/2009/04/a-day-in-the-penalty-box/">the blog post announcing</a> it.  It should also be noted that there is talk between sites on the network and in some cases network wide timed suspensions have been issued where there is problematic behaviour on multiple sties. The timed suspension state locks an account to 1 reputation for the duration of the penalty, allowing the user only the ability to read from the site rather than contribute to it.   </p>

<p>As for action the community can take, it is limited (rightly so) to confidential means (i.e. flags) between users, moderators and Stack Exchange employees.  If you are particularly concerned by a users behaviour then raise a flag on <strong>one</strong> of their posts explaining the wider situation.  </p>

<p>Alternatively if there is a particular piece of content that is <strong>offensive</strong> then you can cast an "Offensive Flag" on it.  I'll admit this is hidden away in the flag dialogue, but is under Flag -> It is not welcome in our community:</p>

<blockquote>
  <p>This question contains content that a reasonable person would consider offensive, abusive, or hate speech.</p>
</blockquote>

<p>If 6 community members (or one moderator) raises an offensive flag on a post then it is deleted and the poster 'fined' 100 reputation points.  This is not an insignificant penalty, therefore please take care to read the description of the flag before raising it or it will likely be declined.  <a href="https://meta.stackexchange.com/questions/22174/how-does-the-offensive-flag-work">Further information on the offensive flag</a> can be found on the central Meta Stack Overflow.  Flags on comments work slightly differently (and without the reputation penalty).</p>

<p>Another option (again only available to community moderators) is to place the <em>post</em> that is causing issues into a (usually temporary) 'locked' state where no actions at all can be taken on it.  This in theory allows all parties to take a step back and cool down from a situation, indeed it was used on the question you linked to.  </p>

<p>Finally, for those <strong>posts</strong> (<em>posts, not users!</em>) that you don't think are adding to the quality of the site you always have your downvote available to you to express your opinion. </p>

<hr>

<p>I hope that the above is a fair summary of the options we have at our disposal, and I hope it helps answer your question. However, I also hope we have little cause to use them in the future as they are never decisions taken lightly.     </p>
