Mathjax is pretty cool but it's also pretty slow if you have many formulas. While it's loading the page keeps rescrolling up and down because the document grows and shrinks. I started noticing the load after already ~30 formulas, quite big formulas though.
Also the distribution is a bit bulky, it consists of over 30000 files. You can remove many of them but then you also loose a big part of the compatibility. While speaking of compatibility, some formulas look kinda weird, but those are very few