I have been using this for about a month and haven't experienced any problems at all in my 40D or Sandisk firewire card reader. If you are shooting lots of bursts with your camera, then go for the faster Extreme III or IV.
Quick, lots of capacity, much lower price than bigger name brands; Very reliable; Set at RAW+Large JPEG and ISO 100 in the 40D, it shows an estimated 957 pictures available
A little slower than other brands; but at about 1/3 the cost