Now, let's say you planned to organize protests in the US, Europe, Russia, Japan or other modern countries. You sure have to be careful, because if you don't ask the government to allow your protest, they will come and arrest you. And they are surely not waiting for you to show up, with some unknown number of followers. They will come to you and have a little talk with you to stop your shenanigans. The internet is easy to monitor, especially when you try to reach a lot of publicity. If everyone can hear you, the government can, too. And they have means to track you down. AND they don't care if you're only a 12 year old boy that wants to protest the closure of a youth centre (read the articles in the guardian or the mirror, if you like).
Yes, anti-terror police is monitoring closely, not only the events in Egypt, but also Facebook and Twitter, for hints of anything similar being planned in their countries. And it's easy. They don't have to go out and talk to people, gain their trust, collect information, tap phones of suspects, intercept mail etc. - nowadays, they can just google.
So be careful, hide behind 7 proxies, or even better, make use of internet cafes (remember wearing a hat in case there are surveillance cameras inside, doesn't necessarily have to be a tin foil hat). But as I wrote in my previous post, all you really need is a cause, and people that want something to happen. If they are not there, or not in large enough numbers, nothing will happen. If they are there, things will happen even without the respective Facebook group.
P.S.: The uprisings in Tunisia and Egypt were allegedly started (or "fueled", ha) by people that set themselves on fire. Hint, hint!