Robert Scoble, Microsoft's celebrity blogger, says there's no such thing as bad publicity and that the only danger from catching slings and arrows is that those doing the firing will someday lose interest in the attack.He's wrong, but I can't help but feel that the man can't help but feel that way: After all, Scoble works for one of the world's biggest punching bags -- personal defense mechanisms are a job requirement.In this case, the conversation centers not on Microsoft but an advertising campaign from General Motors by which people were invited to create their own TV commercials for the Chevy Tahoe. As would be expected, many of the commercials were less than flattering and are enjoying wide distribution on the 'Net, thus calling into question whether the campaign was a good idea or not.Scoble says the GM gambit was a smashing success because it has everyone talking about the Chevy Tahoe.But there's a difference between bad publicity that nonetheless enhances a brand -- and mockery. Had the Chevy Tahoe topped one of those most-stolen-cars lists, I dare say the net outcome would have been a positive one for GM, given how few buyers base their decisions on the prospect of their new ride being swiped. But put the Tahoe at the center of a derisive Saturday Night Live skit and you'll have a hard time getting anyone to take a test drive, particularly anyone younger than your dad.Of course, the marketers at GM had to know beforehand that the do-it-yourself commercials would bring out the critics and pranksters, so they clearly side with Scoble on this question. \u2026 Anyone else have a thought?