Any company that changes its strategy midstream is bound to contend with the incumbent weight of its initial vision. One of the latest companies to encounter such a challenge is social networking site Facebook.

Whereas competitors MySpace and lamented Friendster have always been free-for-alls with the entire online populace invited, Facebook launched, initially, as a place for Harvard University students. Later, it expanded to include college students and, eventually, high school students.

Now that it's opened its doors to all comers and ...