I always made the link to the bug report an answer, but I've also seen people adding that information as comment to the question. We probably should agree on one way to deal with such questions.
So far the general method has been to comment on the question informing everyone this is a known bug then close the question as off-topic if you know the bug report that the person is asking about.
This site isn't designed to handle bugs - Launchpad, or the respective software's bug tracker is, and as such and workarounds or patches should end up on the tracker.
We can't answer a question if it's a bug, the built in reporting tools in Ubuntu do a much better job at collecting the information that developers will need to fix a bug and this is a Question and Answer site, not a bug tracker.
I know the answer has already been decided, but I would like to elaborate my comment, on Marco's answer, and explain it.
Instead of coldly dismissing questions related to bug reports, I want to suggest that instead of [closed] appearing on the question, it should be [bug] with relevant link to the bug report.
It will also be more informative to users with the same or similar issues.
My way would be to put in as much information as I can about the bug with at least 1 link to a bugreport. Then flag it for moderation.
Basically it is how I ended up on askubuntu: I found a solution to a problem and the way the answer was given made me register (concise and to the point with more than enough information I needed to fix it). If it was just a link I would have clicked and never even think twice about the site I ended up on.
Known bug is a too vague category. The bug trackers handle multiple things, from segmentation fault over ugly layout, from feature requests to incompatibilities many things.
The bug-related questions can be about different things, from solving a singular problem, resulting from such a bug, solving the bug, searching for an alternative product without the bug, workarounds for the bug, recovering from bad state from a bug and maybe more.
Just closing as
[bug] is the 'I got a hammer - where is the nail?' method.
Maybe the user has already reported the bug, but it's not enough, maybe he needs instant help. The bugtrackers are full of open bugs, which isn't helpfull for the users.
Closing every question which is related to a bug is undifferentiated and shouldn't be done. Helpful answers are circumvented that way.
Answer with a link to the bug report, and a short explanation of how you found the bug report (if it was easy to find, teach the asker to fish) or how the bug explains the symptoms in the question (if it was not obvious at the asker's level that that bug would be relevant).
Ideally, explain how to work around the bug in the user's specific situation.
Have another state for questions: that of "bug-reported", as a red circle (as opposed to orange - unanswered, grey --answered, and green -- accepted). This would mean that these question would not show up as an unanswered question searchbox, but would still be searchable.
If this were linked to the reported bug, then once it is fixed, the answer can be circled green.
I think you are over-looking something when you assume "the built in reporting tools in Ubuntu do a much better job at collecting the information that developers will need to fix a bug and this is a Question and Answer site, not a bug tracker."
Sometimes the answer to the question is to help a person figure out how to file a bug report. In other words, the standard reporting tools are not always a good fit to the problem.
As an example consider a question where a person's system is dead from an apparent ACPI problem. Are the standard built-in collection/reporting tools currently a good fit for that?
I realize you don't want to become a site that focuses on debugging. But I think there is middle ground where assistance can still be useful.
I agree that bugs do not belong on Ask Ubuntu, even if Launchpad is not friendly to non-technical users for reporting bugs. The Ubuntu Forums should be the backup option for diagnosing bugs not a Q&A site.
However while I think individual questions should be closed, I think that the best response to these questions as a whole should be trying to create more canonical answers on how do identify, diagnose and report possible bugs within specific areas of functionality/hardware/software/etc. Most users are able to identify that they are having a sound problem, or a video problem, or an input problem, or a problem with unity, but beyond that identifying the specific package to run apport on, and knowing where else to look for information that can assist in filing the bug can be a mystery (the ReportingBugs page is useful if you actually know the package name or have a window you can click on, but for bugs in background services related to hardware this is rarely the case).
For example "How to diagnose fan problems" is already on the list of desired canonical questions. I would like to see more topics like this, both to help users who need to file bugs, and also for non-bug questions that would benefit from the the user knowing what information is relevant and what information isn't. I believe that this question from today exemplifies the types of questions we should be answering for (and encouraging be asked by) users potentially encountering bugs.
Even if new users' other bug-related questions are closed, they at least leave more knowledgeable, with a positive experience, and with the tools to properly report their bug (or contribute to an existing report). And more importantly, Ask Ubuntu gets a widely re-usable, searchable how-to.
At first thought, such questions appear to violate the FAQ as being too broad, but I think that the scope could be kept concise by only aiming to answer what the first few steps should be in narrowing down where to look for diagnostic information and how to determine if something is a bug or not.
How is the noob supposed to know to follow the link to the bug report and elevate the status, as in click "this affects me to"? Or to use the tools available? Judging from the recent graphics and speed issues in Precise, there are bugs that (probably) affect many people but are still tagged as only affecting "1 user" in launchpad.
How about sending threads that describe bugs to Launchpad?