I ran into an article in one of my magazines which was talking about the similarities between Sufism and Buddhism. I was interested because I have been reading about Buddhism since my college days, but I had never read about Sufism.
The author was talking about how both are interested in existence and killing the ego to be closer to the Divine. I think the difference between mainstream religion like mainstream Hinduism and Buddhism or mainstream Islam and Sufism is that the latter is more concerned about the inner status of an individual, more so than specific practices. Mystics like Sufis and Buddhists want to be closer to the reality and reason for existence rather than the illusion of world affairs or materialistic gains. I wouldn't want to make any generalizations because I'm sure there are Muslims who care about these as well.
But maybe Sufism as a sect of Islam tries to distinguish these lines between everyday life and spiritual goals more clearly. I kind of see Sufi Islam as more devoted to this spiritual journey than the mainstream religion.