We had one of these just three months ago: https://news.ycombinator.com/item?id=5536734
And there was a great discussion about whether or not it was a good idea to let people vote twice.
From https://news.ycombinator.com/item?id=5537023
The most significant result of this poll is that HN now seems to be past the point where we can rely on an honor system to prevent users from giving junk answers to polls. A few years ago we could. That's an unfortunate change.