What are good MO questions in your opinion ?
What "good" means for you ? Can be various meanings "beautiful", "helpful for research", "exciting" ....

Various discussions have already naturally come to this question
I think it would be valuable to exchange opinions about this in separate thread.

Let me collect some quotes:


JDH Jul 15th 2012
http://tea.mathoverflow.net/discussion/749/relation-between-mo-mse/#Item_12

... If the site should become populated only by super-advanced, highly technical questions, as some seem to have advocated, then I would simply expect the site to whither, with fewer and fewer participants, since even knowledgeable users will find less and less of interest, and so they won't be here to answer those advanced questions for which they do know the answer.

Joseph O'Rourke Jul 21st 2012
http://tea.mathoverflow.net/discussion/749/relation-between-mo-mse/#Item_21

Among the most valuable aspects of MO for me personally has been the instances when knowledgeable mathematicians take the time to post illuminating answers to naive questions, for example:
Why is a topology made up of open sets?
Is the boundary ∂S analogous to a derivative?

"If the site should become populated only by super-advanced, highly technical questions" (JDH), we would lose this enjoyable educational aspect.

quid 4 hours ago
http://tea.mathoverflow.net/discussion/1447/3/evaluation-of-potentially-credible-papers-should-be-allowed/#Item_16

Let me give you an example of a recent MO question that I found a good MO question, while it seems not for writing an article (it in principle could be, but it seems not in the present case):

http://mathoverflow.net/questions/110345/does-a-power-series-converging-everywhere-on-its-circle-of-convergence-define-a-c

There is a clear mathematical question OP found interesting enough to dedicate some time to look (before asking) for an answer. This was unsuccessfull so one asks on MO. IMO this is a very good way to use MO.