The opportunity is not for marketers to pick off the chickens one by one but for marketers to unlearn what they have spent so long teaching themselves. The blogosphere is a vibrant human conversation. If marketers can learn to enter that conversation as humans first, talking honestly about what they care about, identifying themselves and exposing themselves, then they will be welcome in the blogosphere. But, of course, that means they cannot enter it as marketers.
David Weinberger offers some advice in Advertising Age which all marketers would do well to heed. Recommended reading.