There's been an interesting discussion on the infodesign cafe list about a recent attempt by a British Member of Parliament (Nick Palmer) to introduce a minimum type size for 'small print'. On the advice of the RNIB (the main advocate group for the partially sighted in the UK) and the Plain English Campaign, he suggests a minimum of 12pt. This recommendation surfaces from time to time, but is usually unaccompanied by suggestions about what to do about the paper mountain that would ensue.
As several correspondents on the list observed, 12pt type is not a very precise term, and height does not in itself bring legibility... as film posters demonstrate:
I've sometimes wondered why Hollywood stars insist on taller type to assert their importance on film posters. Has anyone ever insisted on a contractual right to legible type?