In the last couple of months I have had......

Hilton Reading - Paid - Standard room to Exec Room - at Check in
Hilton Newbury - Paid - Standard room to Deluxe - At check in
Hilton Edinburgh Grosvenor- Paid (2x twin rooms) no upgrade but given 30,000 points comp which I didn't ask for but was very welcome
Hilton Manchester Deansgate - Paid Queen Room to Exec floor on all 4 of my last stays all at check in
Hilton Glasgow - Paid - Twin room to Exec floor at check in
Hilton Syon Park - Paid - Queen Room to King Syon Exec (and a very nice one too) at check in

All of the rooms have showed as upgraded the day before when I view the reservation online.