I was there for New Year’s 2008-2009 which was incredible. The Lights were amazing… there is really nothing like being out in the interior of Iceland in the pitch black. Black like you’ve never seen even in the countryside… the night we went out was not the most spectacular (I heard from others) of the nights that other people went around the same time but awesome nonetheless. My advice would be to go out the very first night you’re there so you can get another chance if it’s overcast. If you wait til the end of your trip you may only get once chance.