After reading this article on Google Art Project, I mostly have to agree with the author. The web can keep art in front of people who can't get to it easily. It can introduce people to new images and visual ideas. It can act as a refresher course on art you've already seen and started to forget/take for granted. And it has at various times done all these things. But you can't get much of a better understanding just by zooming in on brushstrokes.
There probably are untapped ways to exhibit work online. Something that wouldn't try to replicate the experience of museumgoing, but would actually create a new work in itself. But Google doesn't seem to be going that route.