I also keep my preview window on "sky only" since I do a lot of work with transparencies and reflections. I've also learned to click once and wait(yes, that's true even if no swap file is being used!) and then SAVE THE FILE, then go back to rendering(using the resume render button). It may make it a little longer, saving every few hours or so, but at least you can start rendering from the last save is anything happens. The render I'm doing now started Friday night, and when it's done I'll still not be satisfied with the picture....:)