I'm not at all surprised to see the Nobel Prize in Physics go to Saul Perlmutter, Adam Riess, and Brian Schmidt. The discovery of the accelerating expansion of the universe and dark energy is surely one of the most profound discoveries in science, ever. It's not often physicists realize they have no no idea what makes up 3/4ths of the universe, and it's still extremely puzzling to them 13 years later, as in no one seems to have any idea what dark energy is (if indeed that's what is causing the acceleration --that's how enigmatic the situation is). I don't think the public has grasped this yet (insofar as they grasp any science at all).
I profiled Perlmutter in 2008 for Scientific American. He's a great guy and was nice enough to spend the entire day with me; we talked for hours, had lunch, and I tagged along to one of his classes and to a group meeting. We even talked some about the possibility of him winning the Nobel Prize, and he was humble but knew it would probably happen some day. I doubt he's very surprised this morning, though surely still walking on air.
I'm a bit surprised to see that Permutter won half the prize and Schmidt and Riess a quarter each. I suspect this won't sit well with STSCI, who has done a lot to promote Riess and his work. After my Permutter profile one of their PIOs wrote to me and said, nice article, I just want to make sure you know about Adam's work. Of course, I knew all about it, and mentioned it in my article. Profiling Permutter wasn't a slight of anyone, just the suggestion by my Sci Am editor, Phil Yam, that Perlmutter had done important work. (And, Riess had written about the discovery for Sci Am in 2004.) Schmidt and Riess's group published before Perlmutter's work, but the Perlmutter group had been working on the supernova problem for some years before Schmidt and Riess's group and announced the discovery first. Anyway, some people will probably consider this Prize controversial.
PS: Scientific American also published more of my Q&A with Perlmutter, here, where we talk a little about how credit for the discovery is apportioned.