Can linking to sites that host illegal content be illegal?

I’ve seen many of sites on the internet shut down for this but can’t seem to wrap my head around it. It’s usually a case where a community-like environment offers it’s users the options to post links to other sites that host full-length movies and TV shows.

Is this for real, or are these just cases where the little guy doesn’t stand a chance? It seems the bigger sites/companies who actually host the content never seem to get shut down or imprisoned, rather they get a warning to remove the content, but those people running a site that links to those sites end up in jail. :confused:

What’s the deal? and more importantly, what’s the deal-breaker?

The law on this subject isn’t well-settled.

Here is a discussion of the cases: http://www.chillingeffects.org/linking/faq.cgi#QID152

And a discussion of two recent verdicts: http://arstechnica.com/tech-policy/news/2008/05/linking-to-movies-leads-to-4-million-in-fines.ars

These cases mostly involve:

  1. Links to DRM circumvention devices, which get special legal treatment; or
  2. Sites whose main purpose is to provide links to infringing copies.