This is similar to what I wrote here: http://news.ycombinator.com/item?id=506028 Users should have a history record.
But it won't be an effecient solution, according to briansmith's approach.
Spammers could hire users to comment. Here is how I imagine it: 1- Spammers crawl the submitted article.
2- Ask real users to read it and comment on it.
3- Copy what users said and submit it automatically here.
4- You will think it's NOT a spam, and you will up-vote what the spammer commented, and this will allow the spammer to submit content and the problem won't be really solved/ but reduced.