Matthew,
Thank you for the build, I have now checked it out, and the painting issues in the dialogs disappeared once I had Retina support enabled.
The difference in font quality is like night and day, they are now crisp and beautiful.
Scrolling works reasonably well when you use the scroll bars, but when you use the trackpad, it becomes very jerky, and even worse when you have multiple other windows open. I believe the best way to get smooth scrolling is using the graphics card: draw / update individual lines into bitmaps, and then use the GPU to compose and scroll them. Ideally you should have a 60fps update rate for smooth scrolling, and this is difficult to achieve without the GPU.
Moving around with the cursor is also quite slow once you have more than one window showing, it can take up to half a second to move to the next line
. It seems that you are redrawing every window from scratch, instead of reusing what is already rendered in the other windows. On a Retina Mac you have at least 8 GB of RAM, it would be perfectly fine to use some of it to cache an image of all the other windows apart from the currently active one to speed things up.