OS X Launcher hanging on repeat launches (blank screen, spining beachball)

Since I upgraded to the new OS X Launcher, I can only successfully launch Minecraft intermittently. On most launches, the launcher window shows, but is blank, I get the "spinning beachball" and eventually have to force quit the launcher.

I have tried deleting the launcher and downloading again, this doesn't help.

I would attach useful Console output, but was unable to locate any. However, I am a relatively clueful user who works in the development world professionally; please let me know how I can track down useful diagnostic information for you.