Hello Andrei,
Thank you for bring up this question. It is a question that I will address in the 3rd installment of this mini-series.
In brief, so I don’t give out the whole series now, unidirectionally connected networks are definitely more prone to spam. This is one of the reason that Google+ try enforce the real name policy. Basically G+ is trying to ensure that you are really who you are. Still, that doesn’t prevent people from following a 10,000 users over a weekend, the only thing that is stopping people from doing that is probably due to the negative network effect (i.e. network congestion). Basically if they try to follow 10,000 people, their stream will be so noisy that it would be not usable for the user. So the noise level also serves as a cap on how many people can actually follow.
Anyway, glad to see you back again. I’m glad we fixed that FB connect problem. Hope to see you next time.
