JoBlo, via CHUD, is reporting that the first theatrical trailer for Indiana Jones and the Kingdom of the Crystal Skull will debut on Valentines Day, February 14th. The trailer will likely hit the big screen in front of Paramounts release that weekend, The Spiderwick Chronicles, as well as on TV on Entertainment Tonight.
As JB says, this makes a lot of sense. Exposing Indiana Jones to a younger audience is going to be key to the movies success since everyone 25 and older is going to go see this already - the studio just needs to maintain awareness to get this group and doesnt truly need to exert itself there. But if they can put the movie, and the larger franchise, in front of the kids that are now growing up with fantasy adventure films then it might be able to grow the potential audience significantly.