My guess is that these self interested folks would create many accounts, buy cred with mischievous modding, and make a distributed effort to upmod a particular story. They wouldn't do this to upmod any random story. But news.yc needs to get much bigger in order for this to be a real problem. This is a real problem on Digg.

I'm pretty sure separate accounts are linked via IP addresses. And the one person who will go to all the trouble to spoof his IP address consistently for each of his 10 accounts isn't worth worrying about.

We're small, and we're going to stay small for awhile (hopefully), so this really isn't worth worrying about.