I'll be disappointed if they don't bring Norton back as Banner. I enjoyed The Incredible Hulk, and I enjoyed Norton's portrayal of Banner. Especially given the fact of Marvel Studios actively tying all these films together, recasting one of the major roles is just wrong, even if it is arguably the most minor of the major roles in Avengers.
And to then re-cast everyone from The Incredible Hulk in Avengers...well, what the hell was the point, then?
Besides, do we really expect Doc Sampson to play a role in this movie? For Christ's sake, its already bloated in terms of characters (and likely their respective development in this movie), and I can say that pretty confidantly without having seen a script or even a review. Why add in pointless side characters like him? Hawkeye and Black Widow make sense, but beyond that, I don't see any point in super-hero cameos or name-dropping (though Marvel do love their easter eggs, so...).