It's an interesting situation. The comet orbits the Sun the opposite direction (though also at an odd angle with respect to the plane of the solar system, it seems). This means if it hits, it'll be more like a head-on crash on the freeway than getting rear-ended. And it's on a hyperbolic orbit, so it's going a bit faster than you might otherwise expect. And that also means it hasn't been around these parts often (if ever), which means it hasn't lost much of its original mass like old comets have. Which all adds up to big kinetic energy if it does happen to hit Mars:
Doing a rough calculation, I get an explosive yield of roughly one billion megatons: That’s a million billion tons of TNT exploding. Or, if you prefer, an explosion about 25 million times larger than the largest nuclear weapon ever tested on Earth.
Now, probably this thing's gonna miss. But... couldn't we... maybe... make it hit? It'd be awesome! Think of it as training for that mission to make an asteroid miss the Earth. Yeah, I'm sure pushing a fluffy falling-apart slushball wouldn't exactly be easy, but if my mad plan succeeds, just think of the fireworks!
Okay, okay, but hopefully it'll still put on a pretty show.
Oh, and speaking of comets, Comet Panstarrs has brightened up recently, and is already visible with the naked eye in the Southern Hemisphere. It ought to get a little brighter still and will soon be in Northern skies at sunset.