Bill has an interesting series of posts about Islam and democracy. He makes a comparison to Thomas Paine in quoting Alija Izetbegovic's Islamic Declaration - and my attention was drawn to this specific sentence:
The first four rulers in Islamic history were neither kings nor emporers. They were chosen by the people.
That's a very polemical assertion - not even all Sunni historians agree with this (especially Tabari). For the record, the Shi'a perspective is that the first threecaliphs were usurpers. There was in fact a clear and very public declaration of succession after the Prophet, at the Event of Ghadir e Khum, which is heavily documented by hundreds of sources, both Sunni and Shi'a alike.
But my disagreement is more basic - I shy away from drawing democratic inferences from religious authority models. I think that Islam is democratic, but in the sense that it encourages believers to excercise their reason, and seek knowledge (the famous "seek knowledge, even if in China" hadith of the Prophet comes to mind), and abide by their principles.
But religious authority and doctrine is by definition divine, and opening up that interpretation to a democratic debate becomes a debate on divinity itself. That's fine for theological and philosophical inquiry, but in terms of practical application leads to a weakening of the authority. Ultimately, religion becomes "merely" philosophy and is as easily discarded. But that is not the intended purpose of Islam.
Is representative democracy a requirement of Islam? Not necessarily - the only political requirement for an Islamic state is that each Muslim be allowed to pursue the faith, and that non-Muslims are free to not pursue it. In other words, the basic requirement is freedom of religion, not representative democracy per se - as stated in Ayat 2:256: "there is no compulsion in religion."
Of course, representative democracy and political freedom are not necessarily identical concepts either. There's a struggle for political freedom in Iran, but forcing an American-style representative democracy as a pre-condition is almost a guarantee of failure. But there is at least one representative democracy that does meet the Islamic ideal, and currently ranks in my estimation as the single most Islamic country on earth - The United States of America.