I'm also waiting on Chicago and Stanford. According to Stanford's FAQ page, they invite 20-25 with a target cohort yield of 15. This is purely speculation, but based on the number of acceptances posted here, widely spaced response dates from past years, and the fact that rejections haven't arrived yet, I'd say they're likely still in the decision process. No news is good news.
Cornell, on the other hand has had a very low admission rate in recent years. I did some number crunching from their current student page and assuming no one dropped out or transfered, and I can do basic math (dubious), the recent admission breakdown is: 2012 (12), 2011 (9), 2010 (8), 2009 (8), 2008 (8), 2007 (7). Admissions by study area are also very regular each year, suggesting targets or region-specific funding. Given the number of people already offered admission, I think all that remains is waitlisting.
Anyway, I guess my point is don't assume rejection or give up until you are holding the small envelope (or small email, if such a notion exists).