My A/B test has finished: http://www.gwern.net/a-b-testing#fonts

Baskerville wasn't the top font in the end, but the differences between the fonts were all trivial even with an ungodly large sample size of n=142,983 (split over 4 fonts). I dunno if the NYT result is valid, but if there's any effect, I'm not seeing it in terms of how long people spend reading my website's pages.