I think the fact that a strong portion of their traffic is infringement is pretty damning on liability. While some people will use LimeWire for innocent behavior, or BitTorrent, let's face it, they was developed pretty much to facilitate infringement, gained their fame aiding infringement, and stayed afloat by aiding infringement.

I think the RIAA and MPAA are abhorrent, but I mean... you really don't see how they are liable? Just because they are slime doesn't mean people who infringe on their property rights are magically legally absolved.