BTW, it might seem like idle curiosity as I have no interest in the stats on this site. What it seems useful for is figuring out what types of error and bias there might be in bounce rates on sites I might care about. So thanks for the ideas everyone.
#3 - closing the browser tab would fall under the same category as #2, wouldn't it? GA doesn't know and doesn't care if the user closes the browser entirely, closes the tab or just goes to a page for which google has no tracking (at this point, that would be a text file on the hard drive I suppose!).