I have been using a Hitachi 4gb Microdrive for the past 4 years without any issues (initially on Canon S1 IS) on a Rebel XT. However, I have been getting a bit concerned about it failing at some point given its age. I am interested in getting a high speed 266x (~ 30MB/s writes I think) compact flash card, but can the Rebel XT take advantage of this high speed? If not, what is the maximum speed that the camera itself can take advantage of?

http://robgalbraith.com/bins/multi_page.asp?cid=6007-7699

This link should take you to the Rebel XT data. If not, there is a drop down box to find the camera of your choice. You'll see that there is a bottle neck effect from the body.

While there is a limit to the camera write speed, faster cards may enable faster transfer to a computer.

In my XTi, I've tried several types of cards, but the SanDisk 2GB Ultra II's seem about as fast as the body can take advantage of. I think the Ultra 2 GB II's are ~66X, and when compared to 150X cards (like the RiData), I just can't tell any difference, and I always shoot RAW files. However, the faster cards do transfer files to my computer perceptibly quicker, if that matters to you.

Agreed with Noah + Dean - I upgraded from the Hitachi 4GB MD to the Sandisk Ultra II CF and SD cards and the time required for moving images from card to the HD improved tremendously.

I usually transfer images using the camera. I don't mind the bit of extra time it takes. I am looking at a Transcend 16GB compact flash. Is this compatible with the Rebel XT? I understand that I cannot format the card with the camera (probably need to use windows to format it), but will it work well once formatted externally?