Arthur Phillips, a Minnesota-bred Gen-Xer, earned a similar sum with his debut smash, Prague.  And the youngest recipient of publishings new largesse, local poster boy Jonathan Safran Foera 26-year-old Princeton grad living in Jackson Heightsreceived a clean half-million from Houghton Mifflin (not to speak of a very quick $925,000 for the paperback rights) for his first novel, Everything Is Illuminated.  The magnitude of Safran Foers advance, combined with his tender age, drew so much attention it served to demonstrate to publishers just how powerful a marketing tool the advance itself could be.  The larger the advance, the louder the publishers declaration that this is the book the house is gambling on this season. 