In Arista Records LLC v. Lime Group LLC (SNDY KMW May 11, 2010) - article and a copy of the decision here Judge Kimba Wood found Lime Wire guilty of copyright infringement. Basically, LimeWire did the same thing that Napster did, leaving an evidence trail similar to Napster's but using Grokster technology. Remember the Supreme Court said that peer-to-peer filesharing was a technology capable of non-infringing uses.
So just distributing the technology won't get you in trouble. But using it to actively promote, facilitate and profit from infringement will, particularly where technological measures that would make it difficult or inconvenient to infringe could easily have been put in place. An expert found that 98.8% of the uses of this peer-to-peer file sharing technology were infringing uses. He found that 93 percent of the materials in LimeWire were highly likely to be copyright protected. Over past years, the record companies filed over 6,000 lawsuits against LimeWire users. They obtained 700 judgments and settled 4,000 cases.
LimeWire was launched in 2000. By 2003 it had 2 million users per month. At the time the suit was filed, LimeWire had 4 million users per day.
From 2004 - 2006 annual revenue grew from $6 million to about $20 million. LimeWire's CEO has been held personally liable.
There will be a trial on a number of other issues raised. A troubling allegation surfaced that an attorney from the Electronic Frontier Foundation gave some bad advice to LimeWire regarding a document retention policy.
The short answer is that pre-infringement evidence can be used to prove intent to infringe for those infringement claims brought within the statute of limitations. So documents from ten years ago can show that you intended to promote infringement three years ago.