According to Nick Halstead, the CEO and founder of TweetMeme, they have served 1.6 billion impressions of their retweet buttons in the last month, and are seeing an average 20% growth from one week to the next.

One of the reasons for the popularity of TweetMeme could be their reliability and innovativeness. The features they currently offer include one-click retweets, RSS and email buttons, a range of plugins and 11 URL shortening services. The retweet functionality comes with basic analytics showing who retweeted and linked to a particular story. This functionality is planned to be expanded in a soon to be launched service that will allow their users to judge the performance of a story.

Among those who currently subscribe to TweetMeme are Mashable, PerezHilton and Techcrunch.

1.6 billion impressions, however, means that the buttons are only viewed 1.6 billion times a month, not actually clicked. The number of clicks on a retweet button are substantially lower.

Halstead informed TechCrunch that the actual number of clicks on the retweet buttons was estimated to be in the region of 6 million a month, which amounts to a click-through rate of just 0.375%.

Retweets have become so popular due to the fact that it is much easier to retweet an article than to actually type out a new tweet or a comment.

Blog owners and publishers use retweet buttons partly to show-off the number of times their article has been mentioned by others, but also to prompt more readers to discuss the post on Twitter.

This second reason, though, seems questionable, given the low click-through rate on these buttons. If, in fact, the retweet button gets clicks from only 3 out of 1,000 viewers on average, it could hurt small blog owners more than help them as it would only serve to highlight the low number of retweets.