Originally Posted by
SkiAdcock
A thank you is never wrong, whether it be via PM or via the thread itself.

Agreed.
And let me add another way you can "say thanks" is to just be more active on FT. There are probably Marriott hotels you have stayed at that don't have much written here on FT concerning them. Spend some time and write up a trip report about your trip (and any future trips as well).
Basically, the best way you can say thanks is to give back to the community. ^