Although AT&T quickly settled its legal disputes with Berkeley Software Design and the University of California, legal wrangling over intellectual property claims to various parts of Unix and Linux have continued over the years, often involving byzantine corporate relations. By 2004, no fewer than five major lawsuits had been filed. Just this past August, a software company called the TSG Group (formerly known as the SCO Group), lost a bid in court to claim ownership of Unix copyrights that Novell had acquired when it purchased the Unix System Laboratories from AT&T in 1993.
Hal Varian of Google describes the current situation in patent litigation as one of Mutually Assured Destruction. That is, they way you protect yourself from patent litigation is to acquired some patents yourself, so that you can threaten to counter-sue anybody who sues you. Ugh.