Roam4Free did an analysis of the cost to the economy of Twitter use.

Our figures suggests 27M minutes per day about 450,000 hours/days around 13.5M hours month of non productivity due to our obsession.

Our estimates for 2008 suggest @ a minimum lost productivity cost of $20/hour this will represent $300M/month so $900M for first quarter, $600M per month for 2nd quarter so $1.8B, $1.2b per month for 3rd quarter so $3.6b and $2.4b/month for 4th quarter so $7.2b