U.S. citizens currently in Egypt should monitor international and local media to stay abreast of announcements from the embassy. Due to the fluid nature of the situation and the volume of phone calls to the embassy, U.S. citizens should not wait for a reply from the embassy or the Department of State before traveling to the nearest airport. Cairo airport is open and operating, but flights may be delayed or cancelled, and transport to the airport is disrupted, due to the protests. Travelers should remain in contact with their airlines or tour operators concerning flight schedules, and arrange to arrive at the airport well before curfew hours."
Read the complete Warning: http://travel.state.gov/travel/cis_pa_tw/tw/tw_5267.html