Hello,

>    Can you point me to cool Web sites that use XHTML + SVG or XHTML +
> MathML?

  The Ruby Slide Show (S9) gem that lets you create slide shows and
author slides in plain text using a wiki-style markup language that's
easy-to-write and easy-to-read has a dozen+ samples that include
"loss-free" gradient background themes (using SVG) that may qualify
for "real-world" practical HTML+SVG case studies.

   Samples include:

   o Slide Show (S9) 10-Minute Tutorial  @
http://slideshow.rubyforge.org/s5/tutorial.html
   o Microformats - Add Semantics to Your Web Site  @
http://slideshow.rubyforge.org/s5/microformats.html
   o Facebook Stats, Numbers & More @
http://slideshow.rubyforge.org/s5/facebook.html
   o Merb - All You Need, None You Don't @
http://slideshow.rubyforge.org/s5/merb.html

   (Note, S5 slide shows include a hidden control bar. Scroll to the
lower right corner to make the jump box, outline toggle button and
more show up).

   Cheers.

PS: S9 Tip of the Day: Replace .html with .svg to check your
background gradient theme. Try
http://slideshow.rubyforge.org/s5/microformats.svg

-- 
Gerald Bauer - Internet Professional - http://geraldbauer.wordpress.com