I have been writing (and editing) a number of longer posts¹ with a lot of maths in them lately. Sadly, whenever you change a single character, the whole preview is reset which in particular means that all math has to be retypeset. This is annoying (everything reflows!) and a real bummer on slower machines (think netbooks, tablets, ...); when I edit a longer post I have to wait several seconds (>10s have happened) before I can check wether the syntax was good.
With the techniques shown here it should be possible to let MathJax redo only single paragraphs; that would already be a huge help. In principle, it should be easy to split preview input by paragraphs and only reparse (and mathify) those that changed. Please (have tech) look into this.
Please advise wether I have to take this to meta.SO.
¹ Side-by-side and/or selective preview would be cool, too, but that is for another day.