X-Men: First Class. Fox confirmed Vaughn's attachment today and said that the film will begin shooting this summer (!) in time for a June 3, 2011, release. The movie basically hits reset on the franchise by going back to the twentysomethings who became the superheroes we later knew, "Star Trek" for the spandex set. So casting for said twentysomethings is likely to go into overdrive; if you're a fan of an up-and-comer (or represent one) these will be good and busy times.
All that is positive news for fans, but it really fills up the late spring release calendar for next year. "Mission: Impossible IV" comes out just one week prior to the "X-Men" release date, and the new "Pirates of the Caribbean" is set for release just two weeks before.
As for the Hollywood back story, apparently all of Vaughn's hesitations and the studio's gyrations are resolved; no quote from Vaughn in the statement, but Bryan Singer, who is one of the producers, says that Vaughn has "a deft hand with multiple characters and storylines, and a great love of the X-Men universe."