Quite often actually. Though truth be told, it's less to do with Yahtzee's opinion and more to do with the fact that I had never planned to buy said game in the first place. Unlike you rich Americans, down here in Australia if I want to buy a video game I have to give up a lot of money. As a result on the rare occassions I do plan to buy a game, I need to know that it's worth it.
Most of the time, the games I end up buying are games that I had already planned on buying to begin with, and Yahtzee's opinion isn't going to sway me. I know that Yahtzee is going to hate Halo: Reach, it doesn't stop me from buying it because I knew that no matter what, he always was going to hate it.
I go to Zero Punctuation to get entertainment, and while there are more then a few times his opinion has made me say 'eep, I'm going to steer clear of that', it needs to be worth noting that I never had a powerful desire to play Hunted: The Demon's forge, Red Faction Armaggedon, Fear 3, Catherine, Call of Jurez, The Witcher 2 or most others in the first place.