Turned out you were right. Cards arrived in the mail on Thursday (Christmas Eve). Got a separate mailer with the activation codes four days later(!), on Monday.

Fer cryin' out loud, they send the gift cards, with NO mention that the activation codes come in a separate mailing. But on every card, there's a big sticker that says "activation required - go to this website". On that website, the instructions seem to indicate to use the number on the piece of paper that the cards were stuck to - it wasn't a perfect match, but looked close, and since there was no mention of a separate mailing, why would anyone expect it? Never mind they send the GCs and the activation mailer doesn't show up for FOUR DAYS...

Sheesh.