I very rarely get upgrades, but as someone else said, it is only a bathrobe and mouthwash. I think a lot of it depends on the hotel and how full it generally is. Someone else commented how they don't get upgraded at Marriott Kensington. I've been staying there for almost two years, my colleagues 3 and we rarely get upgraded. We asked the GM and sales director why not... apparently they've pretty much always sold their executive rooms.

I have found you're more likely to get an upgrade staying one or two nights rather than the week - makes sense really as the room is more likely to of been sold for one of the nights if you're staying longer.