Well, the back tire definitely has a flat -- went from 100psi to 20psi overnight. The offending item appears to be a staple that was embedded on the inside of the tire. Probably happened somehow at the shop, since that tube was new & lost air from the start. Bleah.
The front tire seems to lose about 5psi overnight -- it's probably ok, but I'll check that one as well. If they're both solid, I'll try to ride the Marathons at a few different PSI's over the next week before deciding whether or not I need different tires.
BTW Spambait, I do have a floor pump. But I'm not planning to drag it along with me when I tour.
So Brakemeister -- know of any problems using the 20 x 1.5 "wireless" / folding tires on 20 /1.5-1.75 wheels? Folding tires may be very handy as a backup when on tour....