Is it just me or does the Mac App Store beach ball for you?
The answer is simple; the server is overloaded. The 'App Store' application is simply a glorified brewer front end and when it 'beach balls' it is due to the server being overloaded due to heaps of people downloading Lion. Hopefully in a few months it'll die down and things will get back to normal but until then you're just going to have to wait and patient.