I have a non-retina MacBook Pro (medio 2012 model, OSX 10.8.3) that only has USB3.0 ports.
When I insert the DigiSpark, it gets powered, but does not show up. When I use an USB extension cable, the DigiSpark does show up.
How to check for your DigiSpark:
Click the Apple logo at the top left of your desktop, and select "About this Mac".
In the popup, click "More info" and then "System Report".
In the Sytem Report, click on 'USB' in the left column (under 'Hardware').
Insert your Digispark, then within 5 seconds hit Command-R to refresh the System Report.
Your DigiSpark should now show up as 'Vendor-Specific Device', and if you click on that, it will list "Product ID: 0x0753, Vendor ID: 0x16d0" which are the correct numbers for the DigiSpark bootloader. You must do the refresh within 5 seconds, as the boatloader shuts down after that.