The captcha is the biggest problem with that, so I'd say this suggestion would be denied, if only through technical limitations. It's true that you can code captcha solvers, but that's just not the way it should be.
What I'd like to see though, is the ability to have a timer of sorts that shows how long it's been since you've last clicked the link. Storing a cookie on your computer should be enough to do that, from what limited knowledge of how computers work I have (Someone correct me if that's not the case).
It'll also be nice if there were color changes to the buttons. Currently the buttons are green, but it'd be nice if they changed to red after you've clicked on them once.
Both the suggestions I made above aren't related to when you vote, but when you click the button, so it should be too hard, I should think?