McDonald's wants to show that "the customer experience can be really valuable to companies" - by paying people $10 to blog about their experiences there.
I imagine they won't be as happy to pay for negative experiences.
As a geek type, I often get clients asking me how to use blogs. The answer is: not like this.
"Shall we get a blog?" Often the answer is no, even forgetting the above. Like any communication - "what are you trying to achieve?" and "how is it going to deliver value to the consumers that choose to let you talk to them?" are the questions to be asking. Not how do we jump on the X bandwagon.
Why not roll this model out into the mainstream media? Simply pay for laudatory editorial for your company - it's a PR dream. If it's not appropriate for mainstream journalists, its not appropriate for bloggers.
People are your partners. Word of mouth is the advertiser's dream because people believe other people, not advertisers.
But if it's not genuine, you've just hired another paid shill, which means they can't give a genuine opinion, negating the effect you wanted to achieve in the first place.