The force of a gravity hammer will not save you from a terrible fall. That and other Halo Reach myths are busted (and some confirmed) in the newest episode of Halo Reach Mythbusters.
I don't need to know whether airborne beetles can kill motorcyclists, which is a myth the official TV mythbuster people busted recently on TV. But Halo Reach mythbusting? That's more useful to me.
Halo Reach Mythbusters: Episode 5 [Defend the House, on YouTube]