Rachel from Katipo, bringers of Koha, had interesting things to say on the Koha list regarding their decision to GPL their codebase, and lessons learned for others confronting that choice. Among others: "For Koha going open source and GPL has been the making of the project." Her message responds to this question.
Koha thread re: releasing under free license
By dchud - Posted on February 16th, 2002