Though military coups are rare lately, they were once common enough in the Arab world that the phrase "Bayan Raqm Wahid" — communique number one — is actually a cliche in Arabic to mean a military coup. So it's not surprising that when the protesters heard that the Supreme Council of the Armed Forces had issued "Bayan Raqm Wahid" today, and it appeared to indicate that the Armed Forces were stepping in, it's easily understood why the crowds thought the end was near. The Supreme Military Council rarely meets, and hasn't met publicly since 1973, and quite visibly neither Mubarak nor Suleiman was at the meeting as shown on Egyptian TV. Then Lt.Gen. Sami Enan, the Chief of Staff [clarification: I'm told it was the Cairo regional commander], went to Tahrir, told the protesters the Army supported their legitimate demands, and told a --porter that "it's over," the impression grew.
CIA Director Leon Panetta seemed to think so, too, when he told Congress it was likely Mubarak would go tonight. President Obama seemed to expect more, too. Given tyhe close communications between the US and the Egyptian military, one wonders if the Armed Forces themselves thought Mubarak would do more. That's why everyone is wondering if there will be a communique number two. It certainly does look like the Army thought it had persuaded someone of something, and then Mubarak offered half measures.
For those with Arabic, here's the announcement and scenes of the military council meeting.