I recently purchased a MacBook Pro with Retina Display. Shortly after receiving it, I realized that Factor did not support rendering on its Retina Display. Magnified (and blurry) text looks pretty terrible next to the crisp native fonts on these HiDPI displays.
Well, after a series of commits, the latest development version of Factor now supports it! There are still a few minor rendering issues with our newly supported "resolution independence", but we plan on fixing those in the near future.
To use the development version, follow the directions from the README.