The last good flying summer was 2003.
That's true
That summer was great for activities other than flying, too
However I have found every summer since to be similarly OK for flying to places.
2011 has been cooler than 2010 which was cooler than 2009 and I know that directly from the electricity bill on a pool heat pump we have. But cooler temps do not translate into worse flying weather, especially if you are a plain PPL with no instrument capability in which case a lot of hot days are too hazy to navigate using the traditional methods.
Hot hazy days also drag out PPL training in the most frustrating ways because many/most instructors will not let you out solo in sub-5k viz, which is infuriating when you then jump into a plane with somebody else and have a great flight.