When are Tweets Worthy of Your Time?

I started using Twitter about four years ago, dubbing it an 'experiment'.  I continue to use Twitter, in part because some clients and colleagues use it, and in part because it is an easy way to quickly market  my own work.  Clients who have decided to implement 'social' methods internally are working with tweeting as well.  But how can you make if truly effective, without getting all your work lost in the stream ... which is increasingly a deluge?   Some thoughts in Information Management.    Is there a true or even fuzzy ROI here?