There's been a lot of arguing over whether Twitter enables political change, so it's worth noting that Egypt's dictators are sufficiently worried about the microblogging service that they banned it amid increasingly heated street protests.

Thousands of protesters, enraged at official corruption and calling for an end to the rule of Hosni Mubarak, took to the Cairo streets and threw rocks at the police today. Authorities responded with tear gas, rubber bullets—and an apparent internet block of Twitter.com, which is now only accessible in Egypt via outside web proxies. For some reason there's no block on Facebook, recently targeted by fellow North African state Tunisia, even though Facebook has also been used to coordinate the Cairo protests. Maybe the authorities just aren't ready for that kind of escalation yet.