Don't mean to resurrect this thread, but I just tried for another Diamond "Guarantee" at a Hampton Inn in a non-major metropolitan location (so it's not like there is some big event), and it was another no. I sent another PM to the Hilton rep on here, but what is the use of having a "guarantee" that never comes through when you need it? This is completely misleading and false advertising.
I've already maxed out Hilton Diamond (at 50+ stays, 100+ nights) for next year, so it may be time to start checking out Marriotts. The reason I don't is because I find Diamond perks like this useful, but if they're never available, I'll start over on another program. I still have a bad taste in my mouth after the devaluation as well.