Many convential media folks who are used to the 'radio' mode of one way broadcast seem to miss out on the fact that to be successful in social media (especially twitter) one has to remember that this is a two way medium. Unless one engages the audience in two way conversations success will not be sustainable.
A simple metric to analyse this would be what percentage of your tweets are @replies, or the ratio followers to following. If these ratios are heavily skewed then one can be certain about long term unviability - if you don't listen and only talk you are doomed. There are some media folks who don't follow anyone at all! Need I say more?