Twitter is a very powerful social marketing tool, consider it word of mouth on steroids. If you take the time and build your profile, engage in conversation, give opinions, answer questions from other people it can add up. If you have a lot of followers, a simple tweet about a new product, blog post, website launch, etc. can spread like a wildfire.
Say you have 2k followers, tweet out your message and that will be 2k people who will see it. If they retweet it out to their followers it is like a domino effect and can work with great results. Just a matter of taking the time to use it the right way ( do not go out and add 2k people in hopes they follow you back) tweet more then once or twice a day, engage in conversation and you will see the results over time.