well, well, well. I've heard back from Steam. Seems I overlooked it's email reply. i got a nice letter saying the product key has been used, and that I must have bought a used game, and to take it back to the retailer. Looks like I'm screwed.
Of course I wrote back explaining my copy is a new one, and not from a used-item bin. Ididn't want to be rude in suggesting Steam may have been hacked.
Flyby out, and pissed.