I was thinking of implementing a thumbs system, but mine would require a registration thus ruling out the possibility of people voting more than once unless they create a new account to do so. So I was wondering about Urban Dictionary's thumb system. How does it work? I would imagine that my IP would be stored in a database, so people would not be able to vote more than once however IPs do change pretty often and especially when you're on an iPhone. Probably a combination of cookies and IP checking. Can anyone give me a better insight? What would they check for to ensure you don't vote more than once?
The reason I ask is because I may want to make my a public system instead. Maybe even a hybrid, similar to SO where you can ask a question before creating an account and then have the two linked together. I am using PHP and MySQL.