My premium membership ended without any notification. At first I thought that it had something to do with the site update because after the update I was not a premium member anymore. I was not sure on which particular date my premium membership was up for renewal but I know it was somewhere in May 2011. Thus renewed my membership yesterday and received a confirmation that my premium membership will end on April 10, 2012.
I will send contact@geocaching.com an email and see what they can do for me.