Most people know this, but just to be clear - even though the "View Answers" part of the poll is defaulted to "None", I can still view the answers because I posted the poll. I think Gary might be able to as well as a moderator of the community but I haven't had him check. Anyway - I can check the voters and who they are voting for.
For community only votes:
1. Once you join the community and vote, your vote stays in place even if you leave the community.
2. If you leave and re-join, you do not get to vote again. You can edit your previous vote, but you don't get to vote twice.
For voting in general:
If you've ever viewed the answers to a poll, you know they are listed in the order they voted. When you change your vote, your name is moved to the bottom of the list because you are the most recent voter (even if all you did was take a vote away from someone).
Can we tell who changed their votes? Not to any degree of absolute certainty, no. We do monitor the voting to make sure things are on the up and up as much as we can. Unfortunately, some things are out of our hands as far as controls, but we do the best we can.
If you have any questions about voting, please ask them here.
(Also, if anyone noticed the votes from the most recent polls changing a bit tonight, that was me doing some experiments.)