Very hard to say for sure as the fossil record is very sketchy for chimpanzees.
Some suggestion is made for Sahelanthropus tchadensis being the last common ancestor of humans and chimpanzees but it is not widely agreed. Nakalipithecus nakayamai is considered by some as the last common ancestor of gorillas, chimps, and humans. Ouranopithecus macedoniensis is also suggested for this role. Finally you might want to check out Orrorin tugenensis as possibly the oldest fossil of a direct human ancestor.
No, it's concerned with the identification of the genes that make us human, based on the search for those genes that have most diverged between us and our nearest related species.
The article is now available to read for free on their website.
I'll have to check that out. It sounds neat, thanks.
Just a side note: humans are also referred to by some biologists as the third chimpanzee. Chimp, Bonobo, Human. I'm completely uneducated on the ratio of difference between chimps and bonobos and chimps and humans, but I would love to know if anyone has a source.