Upgraded from a Q4 on the 2008 Autumn colours to the unique 8183 (the only Q3 with butler service)
Which followed an upgrade from 8183 to 8018 within 24 hours of a booking - and that was a a single!
And on the last Westbound, I was upgraded - I'd booked Caronia to get on One Deck - not wanting a Three Deck cabin - and was upgraded at the pier to 1059, which was the cabin I had booked for the final eastbound. QG single. Lovely cabin. So I didn't have to change cabins in New York!
And I have yet to not be upgraded on QM2.
Before that I normally picked my cabin (none of this "stateroom" nonsense) and marked it not for upgrade, but that was when we were booking Signal Deck 8001 and didn't want to be downstairs in a QS which would have been the obvious "upgrade". Too much of a risk to leave it open hoping for a Q1, as the QS wouldn't have suited us as well as a Q2.
Now with the current ships, and the identical cabins, it really makes little difference.