Plenty of this goes on already, there are some apps on facebook specifically to do and it just becomes a big spam circle - of course this is with plenty of deception and self-delusion to try and imitate a genuine interest in post content or in fostering some kind of social relationship with the people you're adding or linking.
It gains you some hits and links of course, but few will generate anything more than people giving a disinterested and cursory glance over or desultory comments imitating conversation/debate/interest to generate linkbacks. Consequently any real friends you have added on facebook will start ignoring (or hiding) everything you link to because of your complete lack of quality control.
Each to their own I suppose, but there's something sad about it too - it's almost like those people who feel they have to game social networking sites by adding people they don't genuinely know, or even posting their desperate pleas for adds on 'add me' groups. Needless to say this is normally against T&C (and disrupts the efficacy of the site for genuine users) and happily - like those who link up on social networking sites to pimp their bloggings - ever more of these pitisome foolbags are having their accounts deleted or, as Raincoster pointed out, having their address bozo'd onto a kill list.
*** it has been pointed out over my shoulder that the above could come across as a bit meanspirited to the people who, in the search for a higher friendcount, do claw desperately for complete strangers to pretend to know them. Good. their lonely tears are delicious to me. :P (But seriously, I'm sure they are perfectly acceptable human beings who deserve our sympathy not scorn)