A lot of the examples touted here are meant to make us, to some extent, question art and provoke discussion (or outrage), and by the looks of it, it has succeeded. If nothing else, things like this have broadened the spectrum of what a lot of people see can be art.
I think a lot of art is about teaching us to appreciate the beauty of everyday life. People have given the example of 4'33", a peice which taught me that sounds that I hear every day can be interesting to listen to.
(I know this argument does sound a bit like when you fluke something cool and go "well, thats what I intended to do". I do accept that some of it is silly. While one painting that is a single colour (eg. Black Square) can be an amusing challenge to what our expectations and definitions of art, any single colour paintings after the original are just derrivative)