I agree with astrobio. You should also take a look at source of support of first year students. You can check the number of first year students getting TAships, fellowships, etc... If that number matches closely the number of "accepted" students, you can be pretty confident that the program is just trying to look as if only deities can get into it.
The GradSchoolShopper book is a valuable resource, but you have to be very keen and consider many aspects while looking at it. While its reliability is a subject of debate, I consider it to be much more elucidating that the US News or the NRC rankings. If you are interested in say, condensed matter, you can just take a look at how much money a department has in that area to learn about its strength, or the number of researchers active in that particular area. You can normalize the money by the number of professors if you don't want to be unfair to smaller, high-quality departments.
Good luck... the waiting game begins in a few hours for most of us. I really hope you went through an apotheosis during your undergrad years if you want to get into UChicago astro