Gravity Falls will be premiering in Disney XD in August! I saw a promo for it before during the credits for an episode of Pair of Kings. I forgot the date, but I'm 100% sure my YT buddy will upload it. I mean, he uploads stuff like promos and "for 10 minutes" thingys for P&F, FH, and Gravity Falls. Stay tuned!
UPDATE: Saw the promo again. The premiere date is: August 5, 2012.