"This is the happiest day in my generation," said Ali al-Tayab, a demonstrator who paid tribute to those who died in clashes with police and Mubarak supporters. "To the martyrs, this is your day."At a presidential palace in Cairo, where demonstrators had gathered in the thousands, people flashed the V-for-victory sign and shouted, "Be happy, Egyptians, today is a feast" and "He stepped down."Associated Press contributed to this report.