I think it only matters if u r shooting continuous, since there's a limit to the buffer how much pictures it can hold before it runs out. So the faster the card, the slower the buffer will build up and thus u can shoot more. If you shoot pictures one by one, there's generally no issue at all.
The other issue, of coz, would be the transfer speed of the pictures back into your computer, since there's where the picture must end up ultimately! But that's nothing to do with the shooting itself. :bsmilie: