Recently there was an extensive discussion about closing the questions containing only the problem statement: http://meta.math.stackexchange.com/questions/9201/proposal-discourage-questions-that-are-nothing-besides-a-problem-statement
(At the moment it has 59 upvotes and 11 downvotes; you can judge for yourself whether this already can be considered community consensus. Some discussion is still going on in comments to that question.)
When I checked a few of recently closing questions in the tools accessible to 10k+ users, I have seen that some users have already started doing this. But some questions were closed without leaving any message to the OP explaining what he could improve so that his question can be reopen.
The goal of the proposal was to increase the quality of the questions, behavior like this is not really helping.
Of course, when I find questions like this, I can leave a comment as an explanation. But I think that leaving the explanation of closure should be the responsibility of the people closing the question.
Please, if you are voting to close a question on grounds of lack of effort/low quality, leave a comment for the OP with an explanation what he can improve. There is a suggestion for a comment template in this post, so if you are satisfied with the wording, you only need to copy a paste the text from there. (Added later: Some other suitable comments can be also found in http://meta.math.stackexchange.com/questions/4925/list-of-comment-templates.)
Some users might ignore this, but at least sometimes the OP might willing to the work and improve his question. In such case it is important that he knows, what he is expected to do.