I have been asked to give a presentation about Social Media at a networking event this week. I went back to a presentation I first put together in 2008 and updated it. My first presentation was "What Is It About Twitter?"
My latest presentation is "Build Your Online Brand to Connect With Opportunity"
The bottom line is that services and platforms are increasingly connected so establish your online identity and use it consistently across the different platforms. However, you can't be everywhere so decide which platforms are most important to you and which one you consider home. With that decision make sure you direct people back to your "home." For example, post on your blog and then add messages to Facebook, Linkedin and Twitter that point back to your blog post. You can use services like Posterous or Ping to make it easy to post to multiple locations.
Wherever possible use the same username or screen name across different services. This makes it easier for people to find you.