All I can say is that here in SE Florida since Hurricane Wilma this week, with 6 million people out of power, with my neighborhood as a sample, there must be about 1 million backfed generators hooked up and running. It is not just commonplace; it is the norm.
One neighbor had a (gypsy) electrician install a 4-wire twist-lock socket in his garage specifically for backfeeding through a suicide cord.
Just stand in the electrical aisle of Home Depot for 5 minutes. You will see a steady stream of people buying wire and plugs and asking how to make a backfeed connection.
The same thing happened on a slightly smaller but still massive scale last year after Hurricanes Jeanne and Frances. I don't recall any reports of utility workers or users being harmed by the practice. There were certainly more people poisoned by carbon monoxide from generators than hurt or killed by electrocution from backfeeding or other misuse.