ASP.NET MVC: Structuring Controllers

ASP.NET Preview 5 (available on CodePlex) has an answer for this: the [AcceptVerbs] attribute. Phil Haack has a blog post discussion how it's used.

As for the view data magic key question, it's an interesting problem. If you think of a view as being a bunch of semi-independent components (especially in light of the new partial view support), then making a strongly-typed model becomes less ideal, as the several pieces of the view should be relatively independent of one another.