FAST!!...but check your Mac OS
I picked this card up based on its Read/Write speeds and also for its capacity. I had picked up a Sony A77 and found that I was filling up 16GB SD card too fast (especially if you shoot RAW + Jpeg). The A77 can shoot 12 fps but the buffer can clog up quickly, but with this card the processing time was at least half the processing time of the Class 10 SD card I was using, which means your back to shooting quickly.
I did run into one issue. At the time I was using my MacBook Pro running 10.5.8, and it could not read the card when I attached the camera or even if i used a card reader. I re-checked using my brother's MacBook Pro running Snow Leopard and it worked just fine. I recently got a new MacBook Pro which runs Lion and it also works great!!
So just double check that you're not running anything less than Mac OS 10.6 or you won't be able to copy the files to your machine for post processing.