What about the paper trail? Is this a little slip of paper that the voter gets to show he voted, kind of like a receipt? What if it does not reflect the voter's wishes? Does he go to the poll worker and have his vote deleted so he can revote? Do we really want poll workers to be able to delete votes? If not, what good is it?
A paper trail is used to audit the vote. It could either be machine readable, human readable, or some combination of the two.
Is this a little slip of paper that the voter gets to show he voted, kind of like a receipt?
No. It will be deposited at the polling place just like regular paper ballots.
What if it does not reflect the voter's wishes? Does he go to the poll worker and have his vote deleted so he can revote?
If it doesn't reflect the voter's wishes, it would be handled similarly to the way that spoiled ballots are today. I would image in any well-designed electronic voting machine, a bad ballot would be able to be dealt with. The voter would probably have to sign that it was defective for whatever reason or something. In fact, a properly designed electronic system would display all of the voter's choices before printing. Perhaps it would be set up in such a way that after printing, it couldn't be second-guessed. This would be a problem though if you had paper feed problems, though paper fed through rolls jam much less often than sheet-fed paper.
One reason why you wouldn't want the voter to get a reciept for his vote is because it opens the door for verifiable fraud. Let's say Joe Democrat is offering $5 or whatever for votes for a candidate. If the voter got a reciept, Joe could demand the receipt (that he could check) before paying. Currently Joe Democrat can offer to pay for votes, but what the voter does in the booth is really his own choice. Personally, if I was offered something for a vote, I'd take it and then vote for the opponent.
Do we really want poll workers to be able to delete votes?
They can delete votes now with paper ballots. I believe a fair amount of this happened in Florida in the past couple of elections with the 'spoiled' ballots (overvotes mostly).