I've been staying at the Marriott London Kensington the past 6 weeks or so (I highly recommend it against other London 4* Marriotts) and they have upgraded me to the Executive room every time. I would guess it's about twice as big as the normal room, which is nice around here.

But since this thread is about suites... that's only happened once. I was given the Presidential Suite last week on a night the hotel was overbooked. Quite nice.

I have a Gold level colleague who was upgraded to one of the smaller suites on another occasion.