Do you use Twitter and Facebook to promote your writing?

I ran across a great blog tonight. http://writerunboxed.com/2011/05/23/why-i-dont-count-followers-mentions-google-alerts-or-blog-hits-anymore/

This writer is not a fan of social media except blogging. She is an introvert writer, and only wants to use FB and Twitter for social reasons not for selling a product. That is what they were meant to be -- social networks where people interacted and made friends.

Now we are all told we must have a platform in order to get work published. Although I spend a little time on Facebook and none on Twitter, mostly because I haven't had the time to learn to use it properly, if I had a novel coming out, I'd be out there making sure folks knew about it. You have to, I think.

My blogs are more for my enjoyment than for promoting my work. I want people to know my voice, my online voice rather than my platfom.
The joy of blogging is meeting people you might never see in person, but I can develop a friendship.

I want an editor to look at my blog and see who I am. Of course he can see what I've published, but I hope my posts show the person who wrote those poems, those stories and essays.

What do you think about social media? Does it help sell books?