Yeah, it seems to be the case that they are pin pointing the neighborhoods most popular for selling those links. Those associations can hurt you I think. It's better to just do the legwork and get natural IBLs instead of going for the quick fixes.
There has never been any word about links "hurting" you. They have only stated this is will not help with SERP's. Buying links can still help IMO, you just have to make sure the placement looks natural, the content is relevant and the page isn't spammy. Its always a good idea to know who your friends are.
Funnily enough, I came across Trustrank is use today. It's part of Google's anti-phishing toolbar, apparently. Maybe I've got it wrong but here's a section of code from O'Reilly about the flaws in the anti-phishing toolbar extension for Firefox: