The December 2011 issue of the IEEE Spectum magazine has an interesting article on Unix by Warren Toomey. It includes some material on the origins and evolution of Unix which I have never come across before.
End runs around AT&T’s lawyers indeed became the norm—even at Bell Labs. For example, between the release of the sixth edition of Unix in 1975 and the seventh edition in 1979, Thompson collected dozens of important bug fixes to the system, coming both from within and outside of Bell Labs. He wanted these to filter out to the existing Unix user base, but the company’s lawyers felt that this would constitute a form of support and balked at their release. Nevertheless, those bug fixes soon became widely distributed through unofficial channels. For instance, Lou Katz, the founding president of Usenix, received a phone call one day telling him that if he went down to a certain spot on Mountain Avenue (where Bell Labs was located) at 2 p.m., he would find something of interest. Sure enough, Katz found a magnetic tape with the bug fixes, which were rapidly in the hands of countless users.
You can read the full article here.