It's extremely low-resolution, but this image gives us a rough idea of what The Desolation of Smaug's skin-changing Beorn will look like in his human form. My, what a spectacular mane you have!
The One Ring pulled this image off the back of a calendar and blew it up into its current fuzzy form. It looks like even when he's not bear-shaped, Beorn is on the hairy side.
SD calendar reveals a new image of Beorn? In human form? [The One Ring via Bleeding Cool]