In the current era, receiving knighthood from the Queen of England is a purely symbolic gesture; there is no military or political power attached to the office. Why, then, would several governments respond with "diplomatic threats" (an oxymoron), and riots erupt in different cities, when a poet was recently knighted?
Because that author is Salman Rushdie. For those of you with bad memories, Rushdie became famous, or infamous, in the 1980's, when he wrote a book which questioned some of the beliefs of Islam, and was somewhat skeptical of the Prophet Mohammad. In 1988, several Islamic governments issued orders to have Rushdie killed, and rewards were offered to anyone who killed him. He went in to hiding, and was protected by various European governments.
In mid-June 2007 Rushdie was given the title of knight by the British Queen. This action brought much criticism around the world in many countries with Muslim majority populations. Soon after the news of the knighthood was released protests against the honour were held in Malaysia and Pakistan where effigies of Rushdie were publicly burnt. On June 19, 2007, governments in both Pakistan and Iran summoned their British ambassadors to officially protest the award.
After Friday prayer services on June 22, 2007 Prominent cleric Hojatoleslam Ahmad Khatami spoke to worshipers by broadcast on state radio from Tehran. He addressed the death sentence issued by the Ayatollah in the 1980's against Rushdie, saying "In the Islamic Iran that revolutionary fatwa of Imam [Khomeini] is still alive and cannot be changed."
On June 18, 2007 Pakistan's parliament passed a resolution condemning the knighthood and demanding the British revoke it. The resolution was passed unanimously, then the Religious Affairs Minister told the parliament that "insults to Islam were at the root of terrorism", and said "if someone committed a suicide bombing to protect the honour of the Prophet Mohammad, his act was justified."
It seems that the governments of Iran and Pakistan (among others) are more willing to kill, than to allow anyone to voice questions about Mohammad, or skepticism about Islam.