Remember the voting machines in West Virginia that just couldn't bring themselves to let people vote Obama? Jackson County Clerk Jeff Waybright, who "hates stories like this" was good enough to show Video the Vote how a mis-calibrated voting machine would take a vote for Obama (or anyone) and turn it into a vote for another candidate—and not necessarily John McCain, either, though that's what would happen if you picked a straight Democratic ticket. So yeah, this could definitely happen to you. Waybright actually seems like a really stand-up guy on people being able to vote the way they want, and details some of the measures they're taking to make sure that happens. The machines have confirmation screens, and they'll have techs at the polling places, just in case problems do pop up. It looks like an easy enough fix too—the same machine, when properly calibrated, should work just fine. So just be sure to double check your vote on Tuesday, wherever and however you're voting. [Video the Vote]
to be fair, those machines use an older method of touch screens, where an overlay registers your touch and corresponds it to coordinates on-screen. If that's out of whack (which about the only way it would be is if it were never calibrated at the factory) then something similar would happen. Basically, in this video his touch was off by about 4" vertically. When he pushed Obama, it thought he pushed something 4" lower. When he pushed Straight Democrat, same thing happened, whatever was 4" below was what got pushed.
So, if you find that happening to you, just press 4" above the selection you want. It looks like you'll have as much time to fiddle as you want to get it right before you push the big red "vote" button at the top of the screen.