What is good art?

I had a very interesting conversation with some Belmont students this last week on Art. We were talking about how music is developing and what the difference is between being a someone who plays an instrument or sings and an artist. There is a difference. Just like there is a difference between things that are "created" and art. This raised the question is there such a thing as good art? Of course there are two problems that arise when we ask this question: first how do we define what is art, and second how do we define what is good?
Its difficult for me to really define what is art because it is something that is so subjective. We hear the stereotypical examples of modern and post-modern paintings where the paint was thrown or done with some kind of bizarre techniques. What do most of us say? I could have done that. Of course the illogical thing to that is that we didn't do it, but someone else thought of it. Another question that arises is must art have the intention of being art? If someone makes a chair is it art or simply someone making something? I think that there needs to be the intention of something being created to be art.
The hardest question is what is good in the context of this question? Of course this is something that is extremely subjective. But couldnt we all agree that Beethoven is good art? Rembrandt made good art? So maybe good art is only those that have stood the test of time. Making the Beetles, Elvis, U2 good art?
I would love to hear thoughts on this issue.