ReadWriteWeb noticed what they termed quite a surprise today, that Windows Live Messenger is the second most used app in Facebook (after Farmville, of course) with some 9 million daily active users:
And as Mashable points out, only about 20 percent of the entire 300 million strong Windows Live Messenger user base are able to access the Facebook/WLM integration, making the numbers even more remarkable.
Mashable also quotes Windows Live Director Dharmesh Mehta as saying that over 80% of new consumer computers shipped are pre-installed with Windows Live Essentials (including, of course, Windows Live Messenger), so we can expect lots more Windows Live Messenger users connecting to Facebook in the coming months.
More from Dharmesh on Inside Windows Live