This week we added rocks to our terrains. We're living out our Apollo 11 fantasies as we spend precious delta-v flying sideways to avoid boulder fields! Seen here, a few shots of Gilly, Mun, and Pol.
There's a size threshold below which we don't intend to calculate collision -- that's still in flux, but we don't want your rovers to rattle themselves apart on apple-sized rocks. But yes, the big stuff is collidable.