Down-side: Lots of publicity stuff (both studio- and fan-produced) would be obselete. We Browncoats have been putting "September 30th" all over the place, and so has the studio. T-shirts, flyers, posters, ... Stuff created for Comic-Con a month from now might have to be changed. Eek!
Up-side: My "BROWNCOAT STAFF Comic-Con 2005" shirts which arrived today don't appear to mention the actual release date anywhere (they just say "coming this fall to theatres...", so as long as they don't release _too_ much earlier, it's vague enough), so they're not obselete! Phew!