How does PR, social media and advertising now work together?

The divisions between PR, social media and advertising have blurred in recent years.  I’ve seen ad agencies launch social media campaigns, social media experts launch PR initiatives and PR folks use social media.  They all contribute to building awareness but what is the main difference between each discipline and what specific impact does each have?

Here’s a short but good post that explains how the three disciplines work together and how they differ.  It maintains that PR, social media and advertising work best when part of a solid, integrated communications program.

I personally maintain my own Twitter, Facebook and LinkedIn profiles as well as a blog.  When I work with clients, I primarily use social media on their behalf to monitor industry trends (TweetDeck is good for this) and breaking news that provide opportunity or potential crisis for my clients.  I seldom use social media to grow a company’s reach and reputation.  I figure if it doesn’t  support their business objectives or suit their target audience or match their resources (time and financial), then why invest huge amounts of time?

How is your organization using, managing and integrating these three disciplines?  I hope you enjoy the short post I refer to above.