When browsing various StackExchange sites that I have no reputation on I frequently see great questions or answers. I tend to use these sites frequently, but don't yet have the expertise to answer questions or the need to ask questions.
If I do ever hit the 15-rep level, it would be ideal to go back and upvote all the questions and answers that had helped me. In practice, I will never make the time to actually do this.
Would it make sense to add a feature where:
New users are able to upvote arbitrary questions / answers prior to earning 15-rep;
Such upvotes would not affect the reputation of other users;
Such upvotes would not be visible to any user other than the up-voter herself;
If/when the user reaches 15-rep, these "valueless" votes would become genuine votes.
The goal is to allow new users to lurk for some time, still being able to vote on great questions and answers, with the ability for such votes to later become meaningful once the user contributes to the community (i.e., earns 15 rep).