Originally posted by Aux Buying a faster card always makes sense, imho. If your current camera can't use all the speed, then your computer can. And your next camera will. I personally hate waiting for copying process from card to pc to finish.
It depends how much shooting you do. SD cards don't have a defined life, but much as shutters have actuation estimates SD cards become liable to malfunction after so many 10,000s of images. My policy is to bring in at least one new card with each body (roughly every 2-3 years), and keep the old ones as spares or for additional capacity - cycling into use on occasion to ensure it is working properly. Some folks say you should have only one card that never reaches capacity, but I believe in always carrying at least two cards, and a third if its a major shoot. I think the smaller cards (my largest are 16 gig) tend to be slightly quicker and a bit more reliable way to go.