I first thought it was just me being dumb until I asked about and found loads of people making the same mistake. I have had a GoPro HD Hero for a couple of years now and its been one of the best thing I have ever bought, I use it more than I would have ever anticipated and highly recommend anyone to buy one. Im forever watching all the random videos on YouTube and picking up filming tips and the best places to mount it etc but I always thought that my footage quality was never quite as crisp and sharp or as HD as all the others I had watched. I used to think it was the lighting or something causing it (at least that was my excuse).
Until recently after a little research I never knew that there were different classes of SD card. This determine the speed of which information can be written to the card. In this case how fast video and sound can be recorded. The faster the card is, the better the quality of the footage is. GoPro's will take a class 4, class 6 and a class 10. The higher the class number is the higher quality the footage will be.
Summary of the classes:
Class 2 - Write speed of about 2 Mb/s
Class 4 & 6 - Write speed of about 4 & 6Mb/s
Class 10 - Write speeds can vary from 10Mb/s up to 30Mb/s but you need to check with the manufacturers specification
I have ordered a Scandisk 16Gb Class 10 card which being shipped as I write this. Fingers crossed it will work out as planned. Ill keep you posted though.
To check what class your SD cards are its the little number with a 'C' around it as shown below
I hope this has been of some help