Twitter users average 23 Tweets per Month. I arrived at this figure by mashing-up some other publicly available data:
First, (from GigaOm) Twitter recently revealed that it has grown to the point where it is receiving and distributing 50 million tweets a day, or about 600 every second.
Second, (from TechCrunch & ComScore) According to worldwide comScore figures released on Feb 16th, Twitter’s own site attracted 73.5 million unique individuals in January, up 8 percent from December, 2009 (when it had 65.2 million visitors). Its annual growth rate is still a phenomenal 1,105 percent. A year ago, Twitter.com attracted only an estimated 6 million visitors. (Please note: ComScore only estimates activity on Twitter’s own site. Usage across other desktop, Web, and mobile apps may be twice as large as on Twitter itself.)
Third, (from my Head) the math: 50 million tweets per day x 30.4 average days in the month / 65.2 million users = 23.3 tweets per user per month.
My math should only be used directionally (the methodology of merging two data sources together is fraught with criticism – but in a space where it is very hard to estimate the true audience of a real time application like twitter I thought this would provide some interesting insight.)