Well normally I do contact the hotel with room requests and to compliment people for good service. I only had to contact a hotel once to advise a GM about a seriously bad mattress. I didn't ask for anything, nor did I expect anything, yet he gave me a free night anyway - which I never used.

FWIW - I also found out they keep the emails in our records. The people in Waikiki knew I had an issue with a bed in another hotel and were able to read the entire thing.