Despite some websites linking this camera with class 10 cards any firmware less than 1.5 will not accept recording and playback in HD setting on this camera.
Firmware update is available but only at a 'service centre', I can only find 2 in the UK so I assume you post your camera off to them???
Class 4 and 6 cards work fine and to be honest I see no need to upgrade to class 10 but its worth bearing in mind if you want this excellent product.
I'd check first with firmware is on the shipped camera. Old stock will be 1.0 (like mine)