title: Stopping users voting multiple times on a website
body: <p>I'm planning to add some vote up/vote down buttons to a website I run. This seems easy enough but I want to stop people voting multiple times. One solution would be to make them register before allowing them to vote but I'd prefer not to have to force them to register. </p>
  
  <p>Is there are a reasonably straightforward way of doing this? Checking the IP address doesn't seem like a good solution, since it's possible that multiple users may come from the same IP address. </p>
  
  <p>Cookies might be the answer, but a savvy user could delete the cookie. Any better ideas? </p>