Wired and effects studio WETA have put together this video showing how many of the big battle (and dragon) sequences for the third Hobbit movie were put together. It's pretty good!

A little infomercial-y in parts, sure, but there are plenty of effects breakdowns, as well some interesting info: the fact that Smaug's wings were so realistically modelled that they generated their own airflow, which in turn affected the fires below, almost seems a little too much.