With the current technology behind the interface of Serato DJ, the recommended display resolution is 1280x720. With the release of Mac's Retina displays, these computers are capable of resolutions upwards of 2560×1600, from 400%-1400% of the recommended display.
If you do run Serato DJ using the largest scale resolution of a Retina screen:
Serato DJ may appear as follows:
To avoid this, we would recommend setting your display to the 3rd resolution available:
With Serato DJ then showing as follows:
Now you've got Serato DJ looking good, you can now tweak the Library Text Size (to personal taste), through the "Library & Display" tab of the Setup screen.
We've been working hard on updating the technology our GUI is based on, and we hope to update this at some point in the future.