My i7 Macbook Air, aka My Precious, won't shut down about 85% of the time. When I tell it to, the screen goes gray and I get the spinning gear-wheel, but it does not shut down until I force it to by holding down the power switch. I've let it sit for long periods (10+ minutes) while spinning. It just sits there until I force it off. I have tried killing various processes and utilities I use (I suspected SugarSync, but that doesn't seem to be it), and I've run Repair Permissions, but nothing works reliably and I can't seem to find out what's stopping the shut-down. How can I find out? Is there a log file created during shut-down that might help me troubleshoot this, or something? Would a Genius Bar tech be able to help? All ideas welcome, and thanks.