We already have a thread here: http://www.eham.net/ehamforum/smf/index.php/topic,78342.0.html
It's going to be the same as the regular tests of the EAS, except this time they're going to do it nationally, by sending out a national activation message. That's never been done before, so they'll be checking to see if there's some kind of strange error somewhere which makes a broadcast station's EAS equipment work in a state-wide activation, but fail in a nation-wide activation, for example.
As far as I know, amateur radio is not part of the EAS test. I guess the only thing that might happen, is that in some areas the message might not be clearly labeled as a test, and you might get a few panicked check-ins to repeaters from some guys who hunkered down in their private survival shelters and fired up an amateur radio station asking what's going on with the Nuclear Zombie Holocaust; if that happens, tell them it's a test, but also take note of which broadcast station is involved and notify FEMA or your state emergency management organization. That's the kind of fault that this test is supposed to find.