Twitter is a great way of integrating with your clients and your competitors, for example you can do real live searches now on what is being said every second of the day!
I use monitter.com for this information, track 3 keywords and when you see someone talking about your industry/product you can engage in conversation with them
I have 2,700 followers on Twitter now and my business has got better as a result of Twitter, I am able to network better with Twitter, swap content with other businesses in my area and there is even #tweetups happening here where us Tweeters are getting together once a month to network - all good stuff
Dell is a prime example, making sales of over $2 million, they have deals for Twitter users only and have done extremely well
Many celebrities have Twitter pages now as well (look for the verified account tick) and are using their account to raise money for charities and other amazing deals
Twitter has changed dramatically since early this year, they have yet to monetize the system but I am sure the day will come. You have RT (re-tweets), connect to your Facebook and Linkedin pages and update your status on other networks without having to update so many at once!
This has been a good benefit for me, updating from Twitter to Facebook and Linkedin, MySpace and Bebo!
Twitter is not for everyone but I think it is an amazing piece of software to come out in 2009 - there is a 140 character limit set though so you need to be inspiring