these are not the US presidential elections, so some margin for error would be ok.
If you put in a block for 5 minutes, that would be quite helpful already. You can make that webmaster configurable: webmasters with lots of disk space can make the block for 100 000 minutes, economy version would be a simple reload block with no entry in database. Or only one entry: last vote
As ip's change, and as there are proxies, you should not block one ip for too long anyway. If someone really wants to vote 3 times a day, there is not much you can do about it anyway.
regarding the other replies: most good boards have voting. It is quite popular with users.
The read count is only a good measure for the popularity of the title, they might hate what is inside the post. And, finally, the way you do the read count, it is a better measure for the length of thread than it is for the number of fans that actually read a SINGLE post.
I would rather have a vote, and a "lenght of post in bytes" indicator than the read counter we have now. The length of post helps to weed out the "mee too"s etc.
Those who don't like votes, please turn it off. Still, you might find out your users would love it. If we had votes here, we could find the most popular hacks and hints by simply looking at the top 100 post-usefulness-votes. This would save so much time!!!!! I would not have to ask Eileen each time I need a hack.
By the way, I have a serious upload security problem, can someone write me, I don't want to post this here!!! Emailing scream seems futile ...