Bought it for a Canon 450D SLR. No different in write speed to a class 2 or 4. Maybe a hardware limitation with the 450D. Writing to it from a PC, however, is fine (fast).
So, if you're buying it for a camera, beware - you may not get the speed you're hoping for.
Having said that, the 450D has a memory buffer that takes the first half a dozen photos (CR2 raw) before hitting the SD card bottleneck, anyway, no matter how slow your card is!
To be honest, you'd be better off buying a normal class 6 SDHC card - for this price, you can get a 32Gb one! (Not that there's any point, even with full CR2 raw plus JPG simultaneous shooting - you'd still get thousands of shots on a card that size!
On the plus side, you don't have to wait for ages to read off 8Gb of data, when you plug it into a PC (like you would with a normal class 6 SDHC, and of course, it's a SanDisk, rather than a dodgy unbranded make you've never heard of, so over all, I'm happy enough with it - just not as happy as I thought I'd be - a shame Canon don't cater for cards like this with their EOS hardware!