TITLE: Resubmitting a paper 
QUESTION [6 upvotes]: (Hopefully this question is not too "soft": I asked it at math.stackexchange.com recently and was advised to ask it here instead).  
I submitted a paper to quite a low-rated journal (impact factor less than 0.3) a while ago, partly because I didn't think that my results were particularly good, but also because at the time I was largely ignorant of the significance of journal rankings. After many months "with editor" it has now finally been sent to a referee, but I'm slightly regretting choosing this journal, as recent feedback has given me the impression that my paper is publishable in a much better journal, and I am at the point in my career (starting to look for my first post-doc position) where I really need some good additions to my publication record.
Now that someone is possibly taking the time to read it, would it be considered bad form to withdraw the paper (or wait until the review comes back, assuming it is favourable), and submit it elsewhere? And is it worth the risk? When considering job applications, how much emphasis do people actually put on where a person's papers have been published, as opposed to how many have been published?
Any advice much appreciated.

REPLY [16 votes]: Research mathematics is a small world. It is rather likely that the people who are currently editing and refereeing your paper will play a significant role in the development of your career in the next 5 years or even more. They might not take too kindly to the withdrawal, especially if they think that the move was not really warranted (i.e., if they don't think that your result is really much too good for the journal you submitted). So think to yourself: is this a risk worth taking? Is your result that badly served by the current journal?
As for the impact factor, have you really tried to find out what people think about those? Deans and other paper pushers might put a lot of store by them, and so it's definitely something to keep in mind in the long run, but your colleagues' opinion of a journal is not based on a somewhat artificial numerical construct, so for your immediate future, the actual name and reputation of the journal is much more important than a somewhat arbitrary numerical score. (It is a fact that the math journals with the highest impact factor are not necessarily the most prestigious ones.)

REPLY [9 votes]: A kind of compromise solution: leave your paper where it is, and, given that you now realize that your result is worth more publicity, write a short note (like 1 page or so) where you quote your paper and describe its main results without proofs (possibly, adding small improvements or remarks). A journal expressly aimed to this end is e.g. Comptes Rendus Mathematique, but many other do it as well; your advisor may give you a good hint.