I would like to add that properly, Sufis still fulfill the religious duties delineated in the Five Pillars.
Sufism implies additional methods used to get closer to God. Sufis still should perform
Salat like all other Muslims, for example. They still pay the
Zakat and perform their religious duties.
Hamza Yusuf said that the Sufis always had a fine tradition of being hard on themselves and easy on everyone else. Unfortunately, he goes on to say, the disease of this age is that
Muslims are frequently easy on themselves and hard on everyone else.
The false Sufis, who abandon the Sunnah, are people of deviation within the ummah.
From http://www.haqq.com.au/~salam/sufishar/sufishar.html:
The Shari`ah is of fundamental importance to the Sufi path. This
point is very strongly made by the great Naqshbandi Sufi, Shaykh Ahmad
Sirhindi (also known as Imam ar-Rabbani), in his letters. Here is a small
excerpt from one of his letters, where he clarifies this topic:
The Shari`ah has three parts: knowledge, action, and sincerity
of motive (ikhlas); unless you fulfil the demands of all these parts,
you do not obey the Shari`ah. And when you obey the Shari`ah you obtain
the pleasure of God, which is the most supreme good in this world and the
Hereafter. The Qur'an says: "The pleasure of God is the highest good."
Hence, the Shari`ah comprehends all the good of this world and the next,
and nothing is left out for which one has to go beyond the Shari`ah.
The tariqah ("way") and the haqiqah ("reality") for which
the Sufis are known, are subservient to the Shari`ah, as they help to realize
its third part, namely, sincerity. Hence they are sought in order to fulfil
the Shari`ah, not to achieve something beyond the Shari`ah. The raptures
and ecstasies which the Sufis experience, and the ideas and truths which
come to them in the course of their journey, are not the goal of Sufism.
They are rather myths and fancies on which the children of Sufism are fed.
One has to pass over them all and reach the stage of satisfaction (rida)
which is the final goal of suluk ("travelling", i.e. the Sufi path)
and jadhbah ("overwhelming love"). The purpose of traversing the
stages of of tariqah and haqiqah is nothing other than the
realisation of ikhlas which involves the attainment of rida.
Only one out of a thousand Sufis is graced with the three illuminations
(tajalliyat sih ganah) and gnostic visions, given ikhlas
and elevated to the stage of rida.
(Quoted from "Sufism and Shari`ah: A study of Shaykh Ahmad Sirhindi's Effort
to Reform Sufism," by Muhammad Abdul Haq Ansari, pp. 221-2. Originally
from Shaykh Ahmad Sirhindi's letters, Vol. I:36.)