From Ethan Zuckerman

When I saw Alaa a few weeks ago in Doha, the first thing he did was grab my computer, log into Twitter and, as he put it, “let everyone know I’m still alive.” This is a good thing to do when you’re an activist who routinely gets detained or arrested. Alaa’s Twitter feed includes updates for his compatriots every time he goes to the police or to a demonstration so he can let people know where he is… and if they don’t here from him, perhaps they need to reopen the FreeAlaa blog.

Twitter is also potentially useful for activists organizing a demonstration, as it’s a lightweight mass-SMS sending system, which lets you warn your fellow activists where the police are and what path they should take. Probably not the purpose the designers had, but an excellent use nevertheless.