Having been frustrated at the FIA WEC race by the time it took to download images, I decided to look at my card reader.
Since the Mac Retina Powerbook has USB3, I started the hunt for a compatible reader.

I found that the Lexar was not fully compatible "Does the reader work with a MAC® system?
Yes, the reader works with Mac OS 10+. However, we are aware of the compatibility issues users may be experiencing when trying to use the Lexar Professional USB 3.0 Dual-Slot Reader with the newest MacBooks, and we’re working diligently to provide a firmware upgrade in the near future.".
(at the bottom of this page: Lexar Professional USB 3.0 Dual-Slot USB Reader FAQ | Lexar)

So I decided on the SanDisk instead.
It works like a charm.
Under 4 minutes to transfer a full 16G card of images.
Your mileage may vary, because you may not have solid state disks, but it is a great time saver.

I would hardly have time to warm up from the rain before the images were in Lightroom ready for selection !

Part no SDDR_280-X20S
UK price £35 plus delivery.