Who’s this Joe?

Right the first time. It means "the average person."

You may see it as Joe Public, John Q. Public, John Doe, "the average Joe," Joe Six-Pack (in which case it means the average working-class person), or derivations thereof.

The sentiment President Bush expressed is very often heard as "Will it play in Peoria?" Agricultural and industrial Peoria, Illinois, is the stereotypical last bastion of rural conservatism and resistance to innovation. If something can be accepted there, thinks the advertising industry, it should be acceptable anywhere.

Interesting: In legal writing, "John Doe" (or "Jane Doe" if the individual is understood to be female) is the preferred form when a legal document refers to an unknown person. (This usage goes back at least two, maybe three hundred years, or even longer!) When a second unknown person is being spoken of, they're called "Richard Roe" or "Mary Roe."

Here's a fun list, while the link lasts, of verious equivalents for "John Doe" in other languages:

http://www.words-worth.de/robin/2004/07/would-real-john-doe-please-step.php