It's important because we want to go freaking fast, that's why!
Seriously, we're usually law-abiding citizens when it comes to the speed limit (OK, maybe almost law-abiding), and nothing grinds our gears like left-lane squatters. In our opinion, lane discipline allows traffic to flow easier and makes everyone's commutes safer.
Check out www.driverightpassleft.com the scoop on laws in your state, and maybe grab a bumper sticker or two while you're there. We need to spread the word!