First I wanna say thanks for this great little plugin!
I started using it recently and have a couple of feature requests:
1) Ability to vote on categories, tags and custom taxonomies.
2) Ability to set the time after time the cookie expires
3) Multiple vote categories for e.g quality, price etc.
4) Option to add voting form to comments (however I think it could be done manually at this point - but I didnt try it yet)
5) Option to store user ID's (of those registered users who voted) as an array in another custom field value. That way we could use that data somewhere in the site.