a) From view numbers on the forum, my guess is that 40-50 people follow this forum closely. (Posts with many replies have higher numbers because they get viewes by poeple who already have seen them, to see the new answers.)
b) By the time Gray's first Pontifex poll closed on www.bridgebuilder-game.com, more than 200 people had indicated they had bought Pontifex. Since the poll was anonymous and allowed multiple entries, this number may be high. But keep in mind that not every bb-game user might have answered, and that by now many people have found ChronicLogic directly (through firing-squad, hotu, ntk etc..) and never saw that poll, which would make the real number substantially higher than 200 (I certainly wish this is the case).