Twitter can be used for many things.  It’s being referred to as more of a news platform than a social network.   Ogilvy 360 has a very good slidedeck about Twitter strategies that lays out  who to follow and what content to create depending on why you are using Twitter.

Using Twitter for PR still gives you several possible goals:

• Brand awareness
• Dialog with influencers
• Thought leadership
• Reputation Management
• Crisis
• Event Awareness
• Media Relations