Several astronomers pointed their telescope at Eris to watch it pass in front of a background star. Occultations permit precise measurement of the diameters of distant, faint objects, and it turned out that Eris was much smaller than previously thought, so much so that its diameter may turn out to be the same as, or even smaller than, Pluto's.
An awful lot of the talks in the Pluto session on Tuesday morning, October 5, at the Division of Planetary Sciences meeting spent more time focusing on how bad weather conditions were during the astronomers' attempts to view Pluto as it occulted background stars than they did on any measurements or science that came out from the data.
Since the discovery of 2003 UB313, larger than Pluto, there's been a lively debate going on in many places about what makes a planet. There's now an article in Nature talking about a proposal that would address the controversy