What's Frodo doing in The Hobbit? I don't want to spoil too much, but I can say that Frodo is part of the connecting tissue between The Hobbit and Fellowship of the Ring.
In fact, the next shot was an over the shoulder on Elijah Wood hammering a sign up on Bag End's front gate: "No Admittance Except On Party Business." You guys should have an idea where that puts this moment in the timeline.
Specifically, at the end of the second Hobbit movie so it ends about half an hour before Fellowship of the Ring begins. I don't think linking the two projects is strictly necessary -- is anyone really going to be confused that The Hobbit is part of the LotR saga once Ian McKellan pops up as Gandalf? -- but it's also hardly the end of the world. Anyways, it's nice to have Frodo's role confirmed, lest anyone worry that Bilbo was going to suggest to the dwarves that they take his inexplicably full-grown nephew along to Lonely Mountain. Thanks to Jamey for the tip.