I suppose the conflict of interest would arise if Pogue had been asked by Apple to write up a Missing Manual for Snow Leopard. (Was he? No, afaik, but [citation needed])

Conversely, one might say that he'd decided to create such a manual for Snow Leopard because he genuinely believed what he'd written in his review, and felt the product worthy enough to warrant such an act. But then again, I suppose anyone who reads Pogue's columns/blog regularly would know he's a MASSIVE Apple fan-boy (neutral observation - I'm not judging him..)