There's a fascinating article on Christian Scheidemann, a conservator of contemporary art, in the May 11, 2009 issue of The New Yorker. I'd post a link to the article if I could, but since it's not the current issue, it's hidden in their subscriber-only archives. There are many good parts in the article, but this is one of my favorite bits:
The Guggenheim had recently held a symposium at which conservators examined the minimalist artist Ad Reinhardt's "Black Painting," which had been scratched during preparations for an exhibition and then subjected to misguided attempts at restoration. "It was a multimillion-dollar painting, and it was a total loss -- the painting is totally dead," Scheidemann told me. "It is a good study for other paintings -- like cutting open a body to look at the organs. But you would no more put it on your wall and say it is an Ad Reinhardt than you would unbury your grandfather's body and say it is your grandfather."