Kaveh Bazargan is going to speak about
TeX as an ebook reader at the forthcoming
TUG 2009 conference. He experienced with this
on the Iphone -- see his abstract on the conference
web page.
jsMath is widely used too, is has part of the TeX engine
reimplemented in JavaScript, but on ebook one needs
linebreaking and chips in ebook reader are now capable of running
unrestricted TeX.
Petr