I bought this card for my Canon EOS 400D, and I was pleased to see when I turned the camera on that it cheerfully displayed "1587" to show me how many raw shots could be recorded before I'd have to change cards. Woohoo!
Having bought a 2Gb SanDisk Extreme IV with the camera, I didn't want to spend a fortune on spare cards so I did some research on the web to find out exactly how fast a card needs to be before the write speed of the camera falls short of the card and you are paying for "unused extra speed". I have found it difficult to find accurate sources on the web but it seems that a 133x card should be more than adequate for storing data as fast as an EOS 400D can supply it. Which of course means a less congested buffer and more shots in a row in burst mode!
I have done some simple tests with this Transcend card compared to my Extreme IV, and superficially at least there is no appreciable difference in performance. I have read that the larger memory address space of high capacity cards can slow down data writing slightly as compared to smaller cards, so I will not be going higher than 16Gb. I will be buying a few more of these babies before I go off around the planet!
** Update follows (26 Mar 09) **
Since writing this review I have upgraded to the delicious Canon EOS 40D (see my review on the kit version for the low-down).
The performance of the Canon EOS 40D with the Transcend 133x 16Gb card is noticeably poor compared to both the 2Gb and 4Gb versions of the SanDisk Extreme IV range. Since I do a lot of high speed shooting, I therefore sold my Transcend card with my Canon EOS 400D.
So, if you are a 400D/Rebel user, this card will do fine speed-wise and it is a LOT of storage at a low price. However if you are a Canon 40D user, and you want the full shooting speed, you will probably want a faster card. I have recent reviews on the 2Gb and 4Gb SanDisk Extreme IV cards which will help you decide how fast your cards need to be.