Even though we should not ask, I completely understand your feelings. A few years ago, I gave a gift certificate for a spa treatment to a friend and it cost more than I would ever spend on myself (there was a reason I wanted her to have an extra special treat). She thanked me when I gave it to her, but never mentioned it again. I really wanted to know my money didnt go to waste and wouldn't even have cared if she gave it away; as long as someone used it. But there was no way I can bring it up.
Exactly, so this could just as easily been the subject of a related thread: "Is it rude not to acknowledge the use of a gift certificate?" I would vote yes, especially if it was for an experience (ie restaurant, spa) rather than an object (book, clothing etc.). For a physical gift, ie one that you can see, the recipient can see what it is right away and say, "Oh, thank you, that's lovely! I'll put it on my mantlepiece!" For a spa or restaurant, the recipient can thank for the gift certificate but they haven't really received the gift yet, in a way. If I received a gift certificate for a day at the spa, and then went off and had a lovely day courtesy of the gift-giver, I cannot even fathom failing to at least email the person, or call, or speak next time I saw her, to say "I went to that spa!! Thank you so much, what a lovely gift that was; I had an amazing day!" (Even if it didn't live up to expectations I would say something nice and thank them).
Even though there may have been a thank you at the time the gift certificate was received, for some reason I can't really articulate it seems rude not to thank the person again after you've used it. And to not say anything at all makes the giver wonder whether it went to waste, and I'd be thinking, "Well I guess I won't give them anything nice again."
I do understand wanting to know if/how a gift certificate was used and if the person enjoyed it. But I can't agree that the person is required to follow up on the thank you with a "how I used the card" follow up. If that is needed then what is the polite person supposed to do when they don't like the gift certificate? Are they doomed to be rude?
I can't think of a polite way to say "Aunt Dotty, thank you so much for thinking of us. We gave the gift card from the <restaurant we hate> that you gave us for Christmas to my sister-I am sure she loved it." Never mind explaining that we donated it to charity, which is what DH and I usually do with non-useful cards. Aunt Dotty may not approve of the charity we picked. In our particular case, I am sure that our Aunt Dotty wouldn't approve of the charity. And I will not lie to her and tell her that I loved going to <restaurant we hate> when we didn't. It is more of a lie than I am comfortable telling. I don't mind little white lies, but this feels more like a medium grey one to me. Plus, much as I love Aunt Dotty, I don't want to encourage her to settle on this as the "best gift ever for Lynnv and her DH." At least while she rotates every year, we have about a 1 in 3 chance of actually using the card she gets us.
I am sincerely grateful for her gift and that she thinks of us at all-which I do express. But if being polite requires that I tell her when I use the card and how much I enjoyed <whatever card it is that I hate>, I can't see a way to be polite about cards I don't like.
With physical objects, it is easier. I can thank the person sincerely for the time and effort and for thinking of us. But I don't have to tell them how I am going to use the gift. I can say, "Aunt Dotty, thank you so much for the candlestick you gave us for Dragon Appreciation Day. You can never have too many candlesticks. It was lovely of you to think of us during this busy season. And how is Uncle Spotty doing with his lumbago?" and on from there. I don't have to mention that, while you can never have too many candlesticks, this one is creepier than a roomful of clown dolls. And that I am going to be burning it because I fear that it is going to go all Chucky in the night. And yes, for the record, my own Aunt Dotty has gotten me some of the weirdest and creepiest gifts ever-including a creepy clown doll/candle holder. <shudder>
IMO, a sincere thanks for the gift and for thinking of us is the equivalent of the above thank you. And is perfectly polite and does not require a follow up on how the card was used.