InformationWeek’s Johanna Ambrosio writes about a new GM campaign for the Chevy Tahoe that invites website visitors to create their own commercials and enter a contest. The social networking experiment has had mixed results.

To date, 20,000 ads have been created with about 20% of them negative, a GM spokeswoman says. GM says it’s leaving the ads slamming the SUV on the site along with the positive ones. It’ll be interesting to which ones get mailed around the ‘net. My guess is that a lot more than 20% of the e-mailed ads will be parodies than love letters.

Give GM credit for being willing to take its lumps on this idea. Marketers had to know that they were taking a gamble when they put a massive SUV out for a social marketing experiment just as gas was being forecast to hit $3/gallon this summer. It was the proverbial waving of the red flag in front of the bull. And some SUV critics are taking the bait. Check out this one. It’s funny, but probably not the kind of viral marketing GM wants.

You gotta give a company credit for taking a risk, though. GM could hunker down and play defense but in its current situation, that’s not going to go very far. Good for GM.