I am always amazed how sites can launch and draw traffic. Then add a feature that just takes off. The facebook chat feature that lets you have an IM / Chat session with another facebook friend has over 1 billion messages a day. 1 billion is a huge number. In recent months we all have become immune to million / billion / trillion because of our Nations spending. Don’t let the numbers mix, 1 billion is a lot (I mean a lot) of traffic.
That is just a massive amount of chat sessions. For a any site to get that amount of usage from one of it’s tools or features is a sign that you are doing something right.