We've been using Twitter (@Rokland) for a while now, and find it a great way to keep customers and potential customers posted about new product releases, product updates, sales, etc. It is also a great way for people to send us quick feedback and responses.
The other day I was listening to a radio talk show, and a caller discussed Twitter, his voice dripping with contempt. "Twitter," he said, "is very fitting of it's name, it's filled with people who have nothing better to do than twitter away their time by finding out that their friend just made a sandwich, or their other friend just got home from the gym." Now that quote is not exact since it comes from memory, but it is pretty close.
This sentiment is one I hear often from people who really have not used the service that much (or at all). While some do use the service similar to a status update on Facebook, Twitter allows you to communicate with a broad range of people easier and faster than any other medium. To those that dismiss it in the manner the fellow on the radio, it is akin to dismissing the importance of email by saying "email is just for people who want to read jokes forwarded by their grandmother."