It's not just Democrats in Ohio and Florida who are apparently having difficulties with voting machines. Former President George Bush accidentally voted for Obama! News story here. He apparently mis-entered his vote, and thought that the "Cast Vote" button on the touch screen meant "cast aside this vote". The election officials wouldn't let him do it over, since ha actually cast his vote.
Since he was confused over a supermarket scanner, this doesn't seem too surprising.
UPDATED - Snark tag added by someone else, and I got fooled. I was on Josh marshall's site, and there were these "links you might be interested in" at the bottom of the page, with this story one of them. I hadn't checked out the main page, but the story was VERY well written