Some stack exchange sites (cs, math, physics etc.) have MathJAX support. Now on programmers.se and stack overflow there is less need for mathematical formulae, but they appear, most often when discussing complexities or algorithms that involve some calculation.
I usually help myself with some HTML markup (like "O(n2)" (
O(<i>n</i><sup>2</sup>)), but MathJAX would make it easier. Plus the HTML does not work in comment; all one can resort to there is unicode math ("O(n²)",
O(n²)) which requires copy&paste from something that can type it, because browser can't.
Hm, though we'd need definition for
$\O$, because otherwise it is
The same applies to Stack Overflow. Algorithms are regularly discussed on both Programmers.SE and Stack Overflow.