According to a number of recent posts in Apple's Support Communities and on external Mac discussion boards, some users of the new MacBook Pro with Retina Display and MacBook Air models are having trouble mounting external USB 3.0 drives (or at least they are said to be USB 3.0 by their manufacturers). The drives, from a number of vendors, could be mounted on earlier MacBook Pros, the readers said.
User Micky350 wrote about his/her experience at the Apple Store Genius Bar:
Okay so update: I went to the Apple Store and he tried it on a couple of Retina models and it wouldn't work either. He seems to think it is the cable and the driver from the hard drives thinks it is still a USB 2.0 like the older models and the MBPR are trying to read it as [USB]3.0. He sent the info onto engineering (as he was doing this he came across a USB 3.0 trouble shooting guide because apparently they are aware there are issues and are getting on top of it) but basically said it will come down to 3 options: an update from Apple, an update from each manufacturer, or worst case they just won't be compatible and people that have these HDD with problems will have to buy ones that are known to be compatible.
Some readers reported issues with USB 3.0-enabled MacBook Airs and others apparently didn't.
One reader said that he was able to mount an external HDD on his MacBook Pro (Retina) with a micro-USB cable. I can't verify that.
Let me know if this is an issue for you.