A great idea would be that when you copy a math expression from the browser, it would put the LaTeX code in the copy-paste buffer: f(x) = \int_{-\infty}^\infty \hat f(\xi)\,e^{2 \pi i \xi x} \,d\xi So then I could paste it in an email, in a text editor, in my own LaTeX document, etc.
Not sure if it's just the alt text.
[0] Try http://en.wikipedia.org/wiki/Axiom_of_choice and you get \forall X \left[ \emptyset \notin X \implies \exists f \colon X \rarr \bigcup X \quad \forall A \in X \, ( f(A) \in A ) \right] \,.