I hate reporting errors that I have no way of giving useful information about, but here it is.
Twice now, I've exited the game and the screen goes white. My mouse is still visible, normal cursor, not the game one, and it still moves. The computer doesn't seem to be frozen, but I can't interact with it, or perhaps I can, but I can't see anything. The only thing to do is force a restart.
This very occasionally happened in an earlier version, but hadn't happened in a very long time, and now 0.54a has one it twice in two days.
I'm using a MacBook Pro, OSX 10.6.8, 4GB RAM, 2.4GHz Intel Core 2 Duo, Nvidia 320m. I don't know how to give you any more relevant information, because I really can't do anything once the whitescreen happens besides restart.
Oh, I suppose I should clarify, I'm running the game fullscreen. I suppose this wouldn't completely screw me over if I was running it windowed, so I might try that a few times.