I don't know about _strong_ network effects, but part of the appeal of Facebook (for me) is that it's universal - visitors to the country (e.g. exchange student

I don't know about _strong_ network effects, but part of the appeal of Facebook (for me) is that it's universal - visitors to the country (e.g. exchange students) and people I've met overseas (holidays) are all in one place. Further, it doesn't result in you being introduced to (possibly better) Facebook alternatives in those situations. It may not a strong effect, but there is definitely small cross-country effects IMO.