Personally I'm a fan of bigger font sizes. Interesting though that Facebook actually reduced their body copy down to 11px, and apparently they are doing pretty well ;)
As mentioned before http://fontsquirrel.com is a great resource, which includes a good cross-browser css snippet for embedding webfonts http://www.fontspring.com/blog/the-new-bulletproof-font-face...
On our site (flup.com) we've used Chunk Five as our logo font and Museo Slab as our headings font along with Lucida Grande for body copy. We've also used line-heights and font-sizes from the Blueprint Framework http://www.blueprintcss.org/
Good luck,
Michael.