Why GM doesn't produce food responsibly, fairly or sustainbly
Farmer to Farmer: The truth about GM crops
Farmers discuss loss of markets due to failure of coexistence regimes, the spread of superweeds (including apparently by migrating geese) and the impacts of erosion of choice due to market concentration by companies like Monsanto – even for GM farmers. It gives an excellent idea exactly how big a job hand weeding massive monoculture fields really is, as well as how expenses escalate when weed resistance takes hold. It also shows how non-GM soy can work instead.
See Risky - A hard look at glyphosate for more.