In a WebmasterWorld thread, Adam Lasnik of Google can be quoted on what types of outbound links can and cannot hurt you. Let me first quote Adam;
It's unlikely that your outbound linking is causing your pages to be listed in the supplemental, rather than main index.
Also, be assured that we're not looking to penalize folks for a "bad" link here and there. Rather, our algorithms are tuned to look for patterns of "egregious" linking behavior... both on individual sites and in the aggregate.
With that said, it's certainly in your users' interest that you regularly audit outgoing links on your site (especially prominent ones) to ensure that you're not losing folks' trust by sending them to inappropriate places or 404 pages. Sure, it's great to keep Google happy, but it's usually more important (long term) to have your users be return visitors.
So a link to a bad place "here and there" won't necessarily hurt you, but if "patterns" of bad links are seen, then you need to worry.
Forum discussion at WebmasterWorld.
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