Not that much, surprisingly. The guy really wasn't very subtle with it. I've messed with spoof accounts in my past - I used to have an unpopular forum and I thought it would help raise user activity - and there are a lot of things that can clue you off. In this case, his accounts weren't saying rational things. I dissed the article, and one person would tell me I was being irrational, I'd respond: another person would call me an asshole and a third person would agree and call me a jerkwad. And it all seemed focused around the one thread (I'm a big fan of Rand and Gladwell, and really liked the discussion). All I did was scroll through and look for the anti-Rand people who only had a few points of karma.
Once you have the names, it was just a matter of looking at their comments. In this thread, I said to look at the time between posts: it was a lot easier than that, because I was in class and could just refresh once every fifteen minutes. One name did the talking each cycle, and each time I'd get downvoted one and his names would all get upvoted one.
This was bizarre, though. He was incredibly aggressive about the post, and extremely blatant. On this site, that stood out a lot: usually, people who insult other people get instantly downvoted. That happened to me a lot when I first joined. Here, a bunch of people were doing that and getting upvoted. I just hope this site never becomes diluted enough that something like that fails to stand out.