Keiji has posted on the Messenger developer blog that they have reached A billion requests a month with Windows Live Presence API.

Since then, a growing number of sites like Daum in Korea, and applications like the Windows Live Messenger Facebook application have steadily increased the usage of the API and the control.  We’re happy to report that during the month of August, we received over a BILLION presence requests from all those applications!  That’s over 300 per second on average.  The fact that we hit a milestone like this is amazing when you consider that in the Messenger world, August is typically a slow month, with people on holidays and school vacations.

What is already an impressive statistic is made even more impressive by his comment that it’s over 300 requests per second! That’s really impressive, and shows just how popular this service is.