There are several ways to measure the ROI of your efforts on Twitter. You need to choose clearly defined metrics for how you will measure and rank key criteria. The easiest -- but least valuable -- metric is how many people follow you. While this is a general indication of "popularity," it is not a good metric of influence, customer interaction, or customer satisfaction.

You will want to measure the number of interactions, the number of people you touch, and the net outcome of those interactions and conversations. For example, did you take an initial negative brand detractor and move that person to a higher satisfaction level, or to the point where they have become a brand evangelist?

You might also want to consider looking at the number of mentions of your brand as a general way to measure buzz or velocity as a topic of conversation in the ecosystem.

Also, consider the number of times your content is re-tweeted (noted on Twitter as "RT @yourbrand") and pushed through the network by multiple people. What is the effective "reach and influence" of the people that re-tweeted your content? This is actually an important metric when you look at how often people find your content interesting and "sharable." Interesting and valuable content is more likely to get re-tweeted by your followers.

You should also track the landing page of your site and how many people come from Twitter and what they do once they are on your site. This will help you to determine the behavior of the people that come from Twitter and what they are interested in.