Before you have enough reputation to vote up or down questions and answers, it would be nice if you could cast "provisional" or "pending" votes, that would only take effect when your reputation actually hit that point. They wouldn't be visible to anyone else until that point (except maybe to moderators, and distinguished as such?). That way, OCD people like me wouldn't have to worry about forgetting to upvote a really cool answer we'd seen soon after we joined the site.
This could be implemented either in the StackOverflow software itself, or as a browser plugin. (I don't think you could do it with Greasemonkey because of the persistent storage requirement, but I could be wrong.)