I did the Behind the Scenes Tour on the QM2 in March. Apparently the first one since they started them up again.
I was blown away by it, it was much more than I expected and was worth every cent (which from memory was something like $120). It lasted for about four hours (I wasn't expecting anything near that). We got to see many working areas of the ship (as an ocean liner fanatic I was in my element). Parts of the ship we visited included the docking machinery and anchor area below the bow, the engineering room, the hospital, the galley (which was followed by an afternoon tea in which we got champagne and got to try specialty treats usually only available to Grills Suite passengers), the waste disposal area, the crews rec area and mess, the backstage area and dressing rooms and the highlight - a visit to the bridge and a photo op with the Captain. We were also given some cool souvenirs and keepsakes. I loved it and highly recommend it if anyone has the opportunity.
Get in fast though, very limited numbers. I went straight to the tour office to book it as soon as it was advertised in the program and was told it was already sold out. I told them how much I am into Cunard history and have built models of the QM2 and how devastated I was to miss out etc. They took my name and room number and two days later I got an invitation from the Captain in my cabin mailbox to invite me to the tour.