We have some problems concerning the tracking of votes: Behind our NAT firewall (one ip for every user), it ist not possible for different users to vote on the same image. Something similiar happens when after a maximum of 24 hours, another user gets our dynamic dialin-ip.
The bigger problem: at least here in Germany, logging ip adresses is prohibited by law, despite logging for a maximum of 72 hours seems to be ok.
Using cookies for tracking as an alternative would avoid all these problems. It also might be helpful if the plugin would forget the ip after one day. Would you consider that for one of the next versions?
Also, it would be very helpful to have a classe "voted" assigned to those images a user is not allowed to vote any more.