Limit the number of new stories you can submit per day... the other stories you would have submitted will likely get posted by someone else if they're really worth the time.
That is a good idea. How many stories do you really need to submit in a day?
That won't stop people who are trying to generate traffic; they'll just make more than one account.
Also a good point. Then moderate by IP address.
I've been writing web analytics software for the last couple of weeks, that tracks users statistics, etc. Safe to say that there is no foolproof way to track users who don't want to be tracked.