Tony the tigershark sez:

I believe the m/b manufacturers are working on a std m/b size for these PC's.

Check out [link|http://www.formfactors.org/formfactors/form_factors.htm|www.formfactors.org] -- I think it's the "FlexATX" format you're thinking of (and that both the Cappucino and the Shuttle use).