I forget where I read it, but there was an article about zombie movies verses alien invasion movies. Basically zombie infestations were better than invasions because, with zombies, you could still hang out at the mall, or break into Bill Murry's house and drink his liquor. If there was an alien invasion, everything would get blasted to hell and you'd have to make a drastic change to your lifestyle just to survive. With zombies, just make sure you had plenty of ammo (or a piano for zombie kill of the day) for your trip to the store and gas station.