lucy24 - 12:59 am on Jul 13, 2013 (gmt 0)
it's unlikely that Google can crawl the Facebook page with the link anyway
I've just remembered that this question came up before, and someone pointed to facebook's robots.txt. This is assuming for the sake of discussion that the file shown to a random visitor is the "real" robots.txt shown to named robots. It kinda looks like it.
... and the same for half a dozen other major search engines. Everyone else is globally roboted-out with a comprehensive / (all files everywhere). So "nofollow" is unneeded because search engines never even see the page the link is on, and "noindex" is... uh...
:: twiddling thumbs and whistling happily ::
Can google crawl individual fb pages? If so, they can see exactly who's linking where, even if they're not allowed to visit the page that officially takes you off-site.
In case anyone wondered, the other robots fb considers worth naming are: baidu, msn (but not bingbot by that name), naver, seznam, Slurp, teoma and Yandex. Helpfully listed in alphabetical order.