Until now, I have only stayed with Marriott on LNF rate (or free night promo cert)...across Asia and Europe...From my experience, I think it depends on individual hotels, personnel who you will meet etc...

I had a 3nights LNF stay at Renaissance Naples last summer, and was upgraded from the standard room to Presidential Suite before arrival (after emailing the hotel), thumbs up...Upon arrival, the check-in staff looks confused and we were brought to the suite where the living room is locked, went down to the reception and asked about it, the staff spoke in Italian and giggled before respond to me, well, I felt quite uncomfortable about that. We did get the living room of the presidential suite unlocked, and no issue for the rest of the nights.

All in all, I think it's always wise to look up for LNF, and if you're treated badly, leave a notes with Marriott and they will handle it=)