How to obtain clients IP adress

If your app runs proxied under Apache use this: request.env[ 'HTTP_X_FORWARDED_FOR' ]

Direct requests: request.env[ 'REMOTE_ADDR' ]

You realize most your AOL (and other large ISPs) visitors will appear to be coming from the same IP addresses right?

You might go ahead and store the IPs but then also take into account the time span since the last rating was recorded. If it's less than 24 hours ignore it or whatever.

That's sorta what I do in my free image rating script: http://destiney.com/php#Destiney_rated_images