Hit & Run did the commentary I wanted, so I'll just put the whole thing here:

The New Scientist is running an article entitled, "Earth Without Humans." It asks what would happen to Earth if all 6.5 billion of us simply disappeared.

"The sad truth is, once the humans get out of the picture, the outlook starts to get a lot better," says John Orrock, a conservation biologist at the National Center for Ecological Analysis and Synthesis in Santa Barbara, California.

Just how do things get "better" when you've subtracted the only creatures that are self-conscious enough to know better from worse?

I suppose I'll add that polution isn't really different than poop -- it's value or lack-thereof is defined by humans, in the long run the environment will take care of it, and for the (much more import) short run, we just have to make sure it doesn't pile up in public places and make an awful smell.