MediaPost has an article this morning looking at why some marketers might resist advertising on blogs:

By their very nature, blogs deprive marketers of the control they’ve come to expect: a company’s ad could conceivably sit next to a post ripping its product or brand. Media firms have also expressed concerns about scale, worrying that only a handful of blogs will ever achieve anything resembling critical mass.

Resistance is futile. Control no longer exists. Might as well get use to that fact and get a head start.