Recruiting and engaging brand ambassadors and putting them to work in social media can't be a bad thing, I think, as long as it's honest and open. My guess is that we'll be seeing more and more popular peeps in social media who'll get sponsored by brands. The influence of opinion leaders is obviously leveraged by social media, so if brands approach these people in a correct way and ask them to join forces then we can expect some serious fireworks.
It's not by accident that some of the most successful social media campaigns have used social agents in some way. Think for example about the Ford Fiesta Movement, but also locally the energy drink Burn is showing us how it can be done. On www.burn.be, students can put themselves up as a candidate to become the next Burn Master and go fire up every student party in town. And late at night or in the late afternoon (when awake) they'll reach for their smartphone or laptop to write a quick update on Skyrock or Netlog.
A brand's social presence should be kept alive and nothing's more alive than a real person with friends, activities and stuff to talk about. It's hard for a brand to act like a person, but a brand can support a great person... and come to life! But it's not all fun and games. Authenticity and honesty should always be respected. When failing to meet these principles, the risk increases that the brand gets some serious slamming via comments, discussion boards, blogs, etc. But all this is just part of the game and oh well, in the end, critics are a brand's best friend 
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