Keep in mind that UMDA 7 cards are one of the latest technologies. If your camera is not brand new then you'll likely need to update the Firmware for you camera and some cameras will NOT be compatible with these cards. For example, the 7D needs the August Firmware update to take advantage of these cards.
For the latest generation of cameras the cards are fantastic and maximize performance of those cameras. On older cameras, like a classic 5D, the card's speed will be wasted and the card may not function correctly in the camera.
Don't buy a card rated faster than your camera is designed to operate.