No real help from me but just a note to say that I set up to boot latest 2008 beta for n800 from SD on Saturday and all seems good so far. It seems that you have to be really on the ball to catch the boot options in time, but I just hog the menu key after applying power and almost always get it ok.

The window of opportunity is pretty short though. Is there an easy way to modify the timeout and/or the default selection?