My card is a Verbatim 16GB "Premium" Class 10. It was a freebie I got with the camera, so it is possible the camera shop gave me a cheap one.
I have the camera with me at my desk now and I have been experimenting, and I think I have solved the problem. Maybe this will help someone else one day. Here are my notes: 1) When I switch the camera on, the first shot always takes 10+ seconds to be saved. 2) Thereafter I can shoot away and it only takes about 1 second to save each shot. This is great. 3) If I switch the camera off, and then on again. The first shot will take a long time to save. 4) If I take a shot every few seconds thereafter, then it saves quickly and I am able to shoot again. 5) But if I pause for a few seconds (without switching the camera off), and then shoot again, it takes a long time to save. It is as if the camera (or card?) goes into sleep mode whenever the camera is idle or switched off, and takes a long time to ready itself for saving. 6) I went into the camera menu and changed the "Auto Off Timers" setting. The Standby setting was set to default 6 secs. I changed it to 30 mins. 7) Solved! Now the camera saves quickly, even for my first shot after switching on.