Leading Hotels of the World. (Yes I am lucky!).
While riffling through some of the in-room information, I discovered that they have loyalty program called the Leaders Club. I read through the benefits, and saw that besides getting the usual 'unique amenity on arrival', and late checkout (subject to availability), you also got a free room upgrade, so I looked up online ready to join - finding that there is a yearly membership fee of $100. I have an aversion to membership fees, so I didn't join, and anyway we were half way through our stay.
Then I realised, that if I had joined before our stay, I would have got the equivalent of 5 nights worth of upgrades for $100. Doh! So at this particular Banyan Tree, I would have got $650 worth of value for $100.
So the lesson is - always check the loyalty program before you book, and never make last minute accommodation decisions without proper research.