For wines that lose their primary characteristic when aged (think fruity, fresh wines, normally whites) a screw top is the way to go, for something you want to keep in your cellar and let it evolve a bit till is just right, I'll take cork every day.
As a sidenote, cork was one of the main components of the Space Shuttle's insulation (http://www.nytimes.com/1981/11/03/science/shuttle-s-cork-fro...) [and yes, I'm from Portugal, you can all blame us for the Columbia...]