Twitter is a communication tool and a platform for listening to the communication of others.
Use Twitter to Stay Current
Use Twitter to Network
Guard Your Professional Image
Twitter can be addictive and it's easy to be drawn into the recreational aspects of the tool. However, remember that most employers, many conference organizing committees, and even journal or magazine editors WILL search for you online via Google. Therefore if you do want to participate in the recreational aspects of Twitter I recommend using a separate Twitter account and a pseudonym.
Tip: If you want to convey a professional image then treat all Tweets as if your boss is reading them.