I wonder if anyone at Marvel Studios was expecting the friendship between Tony Stark and Bruce Banner in The Avengers to be so well-received. At the end of the movie the two scientists get into Tony Stark's car and drive off, and millions of fans began imagining what that could mean for Iron Man 3.
The answer, according to Marvel Studios President Kevin Feige, is 'probably not much.' When a fan stepped to the mic during the Marvel Studios panel Q&A and asked whether we'd see Bruce Banner in Iron Man 3, Feige explained where Tony took Bruce:
"He dropped him off at Port Authority.*"
Robert Downey Jr butted in saying he'd love to see Banner show up, but Feige's reply indicates that the script as it stands doesn't have a Tony and Bruce doing science scene (the clips shown actually make it seem like the movie takes place up to a year after The Avengers).
Fret not, Tony/Bruce shippers. Marvel has a long history of last-minute shoots to include cameos and surprises. The schawarma scene in The Avengers was shot after the movie premiered, for instance.iron Man 3 is only halfway done shooting, and there will be plenty of time before it is released. It seems very possible that between now and the release of the movie there will be a scene shot to give us a sense of where Bruce Banner went, but don't expect him to be involved in the film in any major way.
* That's New York's big bus station.