I'm not sure how they do it in other counties or states, but here in Harris County you have to show your voter's registration card (or TDL, but the card's easier). Then once they find you on their computer, a label is printed out and handed to a second clerk. The second clerk puts that label into a book, and you sign it. Then an access code is printed out and given to you. Once you enter the voting booth, you must enter the code to acutally vote. Once you're done, you are given the opportunity to review your ballot and then hit the "cast ballot" button.
It seems like a fair and honest system to me, and I don't really see how you can poll hop to vote early and often in a system such as this. I realize it may work much differently in other places.
Actually, that sounds pretty tight.
I voted in Texas, League City actually, in 1995. I had just moved to the state and wasn't even registerd to vote there. They gave me a provisional ballot, but I couldn't see how it could be crosschecked.