I was thinking about it a little. There is a chance that Smaug will make a brief appearance in part one. Peter Jackson did use a few flashbacks to earlier times in the LotR movies. And telling the tale about how the dwarves got kicked out of their fortress would be a perfect time to do one. Though I'm sure that if P.J. goes that route the glimpses of Smaug will be quick and fleeting. Probably a quick flash overhead amongst flaming trees and blasts of fire. Regardless, I doubt we will see him in his full diamond studded glory until part two.