I've gotten them a few times. I don't drink a ton but I don't mind the occasional drink on a long flight or a short one if I'm not driving at the end, it's a nice little perk.
Basically you need to go into your Rapid Rewards acct and I think it's communications you go into...anyway there is a button to click that you tell them it's okay to send you drink coupons.
I went in and changed my mom's as well although she has not received any yet, but I fly more then her.
I actually have some left over from the last year. They've expired but they never seem to care if I give them expired ones. I've also used up my coupons buying my travel companions a drink as well and they seem fine with that.