Others say...

"Fast and Reliable"
I ordered my first Sandisk Extreme 4 along with the Firewire reader. It delivers on the 40mb per second specification and I have never had any problems with pictures getting corrupted. I ordered a second card earlier this year.

I have dropped this card in the snow, taken pictures for several hours in -15 degree weather, had it in very hot and humid conditions and never had a problem. When shooting RAW I can fill up both cards quite quickly, and when I get back home I really enjoy downloading with this setup, when I have to use other cards or readers I can see how spoiled I have become.

When I switched to Vista x64 I thought I had a problem with the reader, but I called the special tech support number for Extreme products and got to a knowledgeable and understandable tech. He walked me through the troubleshooting and now everything works great.

I do use other cards, but when I am going into unusual conditions, or know I am going to be shooting a lot, I always put this card in the camera.

"As fast as the camera can use"
Ducati cards are faster to transfer from the card reader to the computer, just as these Extreme IVs are faster than the Extreme IIIs. But they are all the same in the camera. Extreme III is as fast as the camera can write the photo. The speed advantage comes when you are uploading 8 GB from the card to the computer. THEN you will appreciate the 10 minute transfer time instead of the 30 minute transfer time. You'll need a firewire reader to take advantage of that speed in transferring to the computer though.... SanDisk makes a good one

"Defective card"
I have always used sandisk CF cards. I bought this for my new Canon 40D and right away I started to see that one out of every 100 images was corrupted. First I thought it was the new camera but soon the camera started to freeze on me when in continuous shooting mode. I thought I might have a bad copy of the 40D! Did some research and found that the same issue was faced by others and the issue was the card and not the camera. I replaced it with an EXTREME III 4GB card and i have not seen the problem since even in continuous shooting mode. I'd recommend sticking with EXTREME III series for now!

"Speed"
I use this card with my Nikon D300 shooting RAW files of about 15MB each. It's a tad slower than the original card (300X) that came with the camera but not noticeable at all when shooting. I still need to take a closer look at the number of frames shot when shooting continuously.

Overall I'm very happy. It's a speedy card and would buy it again.

"up to you"
if you need the specs that this card offers, go for it, if not, there are far cheaper alternatives.