I've written a script that lets you insert dollar symbols automatically(via a keyboard shortcut or button) in the editor window on Stack Exchange sites that support MathJax. You guys also get a special NP
button(Alt-S, S for sansserif) that encloses the selection in $\mathsf{...}$
.
Also, note that Alt-Z lets you exit math mode--this lets you type math smoothly. For example, you can use Alt-S, type PSPACE, and then use Alt-Z to bring the cursor out of math mode, where you can continue typing. (It's been a big help to me on chem.SE, with the \ce{...}
button--I can type chemical formulae within the flow of the code).
Also, you have Alt-O for Big O notation, but I doubt you'll use it.
Feel free to check it out!