I'm going to disagree a bit and say that if it's a recipient I expect to be buying for again, especially multiple times in the future, I'd very much like to know if a gift won't be used. Suppose I have a wonderful little corner shop that makes custom made soaps and lotions. I love the shop and I love the soaps, so I tend to buy them as gifts for friends. I buy gift baskets for birthdays and little personal-sized lotions to keep on hand as "thank you" or "just because" gifts. If my sister-in-law turns out to be allergic to the soaps, or if she's on a soap-free hygiene regimen, I'd like to have a heads up before I give her more soap. I know it's the thought that counts, but I really, really want to buy people items they are going to use and love.
I think the re.lationship makes a difference. If I'm buying someone gifts on a regular basis, I would hope that we had the kind of relation.ship where the recipient could say, "Lori, thanks for thinking of me with the soap, but you may not have realized that I am only washing with spring water and playground sand these days."
If the recipient is a neighbor or acquaintance that I will rarely buy for, I think we can keep the personal details personal and get along with a heart felt thank you.