It might also be referred to as Islamic mysticism. While other branches of Islam generally focus on exoteric aspects of religion, Sufism is mainly focused on the direct perception of Truth or God through mystic practices based on divine love. Sufism embodies a number of cultures, philosophies, central teachings and bodies of esoteric knowledge.
Sufis are active in a diverse range of brotherhoods and sisterhoods, with a wide diversity of thought. Sufi orders ("tariqas") can be Shi'a Islam, Sunni Islam or both.
Often the Sufis and the Shia are attacked by the Selafist or more radical sects of Sunni Islam. Recently a Somali group calling itself al Shahbab (the youth) were filmed destroying shrines of other sects of Islam and those of other religions, including popular pilgrimage sites in the portions of Somalia that they have overtaken. Like the Taliban who are educated by Mullahs who preach violence throughout Pakistan and Afghanistan they seek to destroy any record, houses and relics of any other religion. Women become nothing more than chattel and are denied any education.
Their are also several scholars of Sufism who believe it is not a branch of Islam like the Shiater, Sunnis or the Ismalis since some say that Sufism existed before the advent of Islam. Their is also a mention of Sufis at the time of Moses and Jesus. Also, some consider Socrates a Sufi.
For a detailed history of Sufism see Wikipedia for more on Sufism.
Sufi Shrines Destroyed
A report from Al Jazeera NEWS AFRICA: Somali fighters destroying shrines (December 2008) Click to see the whole video - 
Somali fighters used hammers to destroy the graves of clerics and other prominent people in Kismayo. Al-Shabab, an armed group fighting the transitional government and Ethiopian forces in Somalia, is desecrating religious shrines in the south of the country, Al Jazeera has learned.
The ancient graves of clerics and other prominent people are among holy sites being targeted by the armed group in the port city of Kismayo.
Al-Shabab took control of Somalia's third-largest city about four months ago and quickly announced it would not tolerate anything it deemed un-Islamic.
Recently, the Taliban in Pakistan attacked several shrines of Sufi saints. The Most famous of them is of Rehman Baba, a 17th century Sufi (Pathan) poet, revered in both Pakistan and Afghanistan, whose Mazar and a nearby Majid was attacked as the caretaker was praying in the Mosque of the complex. In Buner the Shire of Pir Baba was held by the taleban until the area was reclaimed by the Army of Pakistan.
One Sufi Hazrat Mian Mir is said to have laid the cornerstone of The Harmandar Sahib Sikhi's most venerated shrine. Known around the world as the Golden Temple because of the Gold applied to its upper story and the Domes of its rooftop, like the Sufi Shrines in todays Pakistan, it too was damaged several times by Muslim's who had little regard for the teaching of the Qur'an.
Music and singing in praise of the "One God" played an important part in Sufism and the founder of Sikhi, Guru Nanak and his companion Mardana ( a Muslim bard of the Mirasi caste) on the Guru's Udasis traveled much of the known world of their time singing praises of God.
No better description of what these men spent their days and nights doing as they crossed jungals, mountains and plains can be given that the words of Guru Nanak as scribed in the Guru Granth Sahib:
- “Me, the bard out of work, the Lord has applied to His service. In the very beginning He gave me the order to sing His praises night and day. The Master summoned the minstrel to His True Court. He clothed me with the robe of His true honour and eulogy. Since then the True Name had become my ambrosial food. They, who under the Guru’s instruction, eat this food to their satisfaction, obtain peace. By singing the Guru’s hymns, I, the minstrel spread the Lord’s glory. Nanak, by praising the True Name I have obtained the perfect Lord.”
- (Guru Nanak, Pauri, pg. 150)
The Taleban of Afghanistan (Pakistan and al Shahbab?) destroy Musical instruments and even kill musicians who do not heed their warnings to find another line of work. In Afghanistan they even killed songbirds that people kept as pets.