Just a heads up to everyone.

Recently I almost lost hundreds of dollars because a hotel employee incorrectly processed my Marriott Gift Card (MGC). And this was far from the first time I experienced a problem at the Front Desk getting my bill paid with a MGC. At checkout, the Marriott employee took an extraordinarily long time to process it and got defensive when I politely mentioned that if it was a problem figuring out how to use it, don't worry about it because I needed to get going to get to the airport for my flight. But finally she said it was all taken care of and the card had been used up. By that time I just took a quick glance at the bill (she kept the card to throw away), seemed ok and dashed off to the airport.

Only later when I looked at my credit card account online did I realize that my Credit card had been charged for the full amount and the gift card had not been used at all!

I subsequently found that:
1. The MGC telephone instructions to report to them if a MGC is lost or stolen apparently is just for show (I'm referring to the message you get when you call them, the back of the card does indeed say it is not replaceable). They will do nothing to try to invalidate a lost or stolen card and enable the owner to get a replacement. They were very emphatic about this. No waiting a year to see if it is used before it expires, no blocking of its use by another party, no nothing.
2. It only is through rather an extraordinary level of service offered by the hotel's management that lost value can be recovered, because there is no way to prove what the value of your card was or even that you presented it at checkout. It ultimately came down to the hotel being willing to make up for what happened, even though there was no physical evidence of what had happened.
3. All of this means it is much riskier to use a MGC than a credit card (for which the consequences of it being lost or stolen are generally much, much less severe).

Given the multiple incidences of Marriott employees having a great deal of trouble processing a gift card in my experience, and the significantly greater risk of using MGC versus a credit card, I won't be using them in the future if I have a choice. Hopefully, at some point, Marriott will fix these issues which make the use of MGCs so not worth it for me. I would refer Marriott to a model where some subway cards are fully replaceable if lost as long as you register the card number online when you purchase it. Surely Marriott could do something like this with their gift cards.