Update 07/02/2013: Google giveth, and it taketh away. MathML support in Chrome has been disabled until it’s “production-ready”.
Putting maths on the web has always been a tricky proposition. Typesetting notation is a highly complicated procedure, so for years people have got by either by compromising on aesthetics and writing equations in plain, unadorned text, or by using off-line LaTeX compilers to make blurry images of what they’re trying to say.