While I think social networking sites like MySpace and Facebook have many benefits, I wouldn't attempt to use them to promote services or products if I were a business person.
I'm a member of both MySpace and Facebook. I use these social networking sites to keep up with friends and chat to like-minded people who share my interests. Most of the people who use these social networking sites do so for similar reasons. Social networking sites are predominantly about socializing via the internet. Although I have a MySpace blog, I do not use it to create a buzz around advertisers. Instead, I use it to write short, humorous articles about life and people with the sole intention of making my friends laugh.
Since I've been a MySpace memeber for quite a while, I know that many of the individuals who use this site do not appreciate it when people use blogs, bulletins or forums to create a buzz around advertisers. In fact, most people find it very annoying.
If you wish to promote your business, use a company that specializes in social media optimization. Social networking sites are meant for socializing with friends, not promoting various business ventures. Let's keep them that way.