1) This video demonstrates some features of MathML in Firefox/Linux.

2) You can zoom in without losing rendering quality.

3) You can find text inside formulaes, with the usual user interface.

4) Native rendering works without extra resources (e.g. javascript or images) 

5) You can specify a different CSS font-family to render formuales.

6) A native implementation gives efficient layout and automatic reflow.

7) You can copy and paste formulaes in other applications.

8) Information can be properly exposed to assistive technologies.