I've created a new proposal on Area 51 for a Stack Exchange focusing on the history of mathematics and science.
As a math student, I am constantly studying the history of the subject. I feel that ultimately, it's the only way to really get a sense of that all important holy grail of mathematics learning: motivation. As for science, studying the history of the subject overlaps very strongly with appreciating the evidence for modern science, since all of the experiments and mathematical arguments were done a long time ago and are seldom mentioned nowadays outside of histories of the subject. And all of this is aside from the fact that the history of science is inherently interesting.
In both cases, mining the literature alone can be very difficult at times, and an SE would be really beneficial. I also hope that this SE might promote the study of the history of science and math among both students and teachers, since I (and hopefully you, too!) really think it's almost crucial if you want to really understanding either subject.
This SE is different to history.SE firstly because it's more specialized, but more importantly because answering or asking questions about the history of science will usually require knowledge of science (or math) as well as just history. Asking about the origin of $p$-adic numbers is unlikely to get you anywhere on a site full of people who are primarily interested in history and not math.
This SE is different to math.SE or physics.SE because an interest in history (let alone an in depth knowledge of it) isn't necessarily standard among math or physics experts, so a question about any even slightly obscure topic in history is unlikely to get a very good answer unless the right person happens by.
I invite anyone interested in the history of math and science to follow the proposal on Area 51, vote up example questions that you find interesting, and post your own example questions.
Meta discussion on physics.SE: https://physics.meta.stackexchange.com/questions/5494/area-51-proposal-history-of-science-and-mathematics