Meanwhile Chrome and IE still don't support MathML. Now that is annoying.
Is MathML actually widely used? I can't believe anyone would really want to use something else than the LaTeX stuff for typesetting formulas. There's nothing as pretty as LaTeX for that. Recently I wrote a small tool that enables me to write LaTeX code directly in HTML and the tool then renders the LaTeX code in PDF, converts it to SVG and places an appropriate img-tag with the reference to the generated SVG. I was u…
1) Working find-in-page that lets you search equations too.
2) Ability to select, copy, paste the math bits.
3) Better accessibility. LaTeX in alt text is something, but actual semantic markup would allow the UA to present things to the user the way the user wants more easily (e.g. without having to re-parse the LaTeX).
4) Ease of editing and reuse (c.f. view source).
5) Ease of styling (e.g. you can use colors to highlight parts of an equation as needed and change it dynamically; some teaching sites put this to very good use).
Note that there do exist LaTeX to MathML converters, so you can still author in LaTeX if you want and export to MathML.