A couple of weeks a go, Fred Stutzman, a PhD candidate at UNC published a brief analysis of Facebook usage by the incoming freshman class at UNC. There have been numerous posts in blogsphere on the paper, including one by Stowe Boyd.
While I think the analysis is interesting, especially in the pop culture insight it delivers, the most critical number was right there in the initial paragraph:
"…I found that 88 percent of freshmen on the UNC campus had active Facebook accounts."
I assume this rate is similar at other universities, and I am blown away.
UPDATE: In fact, at UT Austin (my alma mater), the rate is 90%.