Comments following an article posted by Dennis M. Wright (e.g. Molly Leonard and mattmc3) discuss the issue of GM contamination and subsequent litigation. A comprehensive report on this was produced by the Center for Food Safety (CFS) in 2005 (http://www.centerforfoodsafety.org/Monsantovsusfarmersreport.cfm). I summarise some of their findings here.
CFS chronicled the impact of MTAs (material transfer agreements) between Monsanto and US farmers. According to CFS "[f]armers who discontinue their use of Monsanto's genetically engineered seed face patent infringement allegations in the event that some of that seed from the previous year sprouts "volunteers" in fields converted to conventional varieties" (p. 20 Center for Food Safety, 2005) or farmers who purposefully saved seed.
The MTA between Monsanto and the grower states that the grower accepts the terms of the licensing agreement "by signing this Agreement and/or opening a bag of Seed containing Monsanto Technology" (2006 Monsanto Technology/Stewardship Agreement). If Monsanto considers that a grower has infringed on its patents, the grower may be liable for restitution including Monsanto's court and legal fees. Growers are required to answer claims exclusively in the US District Court of Missouri or the Circuit Court of the County of St. Louis, near Monsanto headquarters.
The CFS reports that Monsanto has 75 employees and devotes US$10 million annually for the purpose of investigating farmers, including its former customers. The CFS provided evidence of between 475-600 investigations by Monsanto annually, with settlements estimated in the millions of dollars. CFS found that Monsanto has filed 90 lawsuits across 25 US states. The largest judgment in favor of Monsanto is reportedly just over $3 million, with a cumulative total of $15 million.