To follow up on the slight difference between the email (chase.com/addcard) and the postcard (chase.com/adduser), I got both communications so I'm sure either way is just fine.

To address the issue raised above by TrueBlueFlyer, I don't think there are any fees associated with adding a user; otherwise we'd have heard about it. There is language in the card agreement for a possible service fee on two or more cards and/or expedited shipping, but it also mentions in the same paragraph that any such fees would be clearly stated before the service was initiated. I suspect they're referring to duplicate cards under the same name. Anyway, very unlikely there are fees associated with this promotion, but a great question to toss out there nonetheless - thanks!