He was, it seems, one who believes that all religions lead to the same God, and hence no one need leave the religion of his/her birth. It is unclear to me whether no one *needing* to leave the religion of his birth is the same as no one *should* leave the religion of his birth. I'd have to do more reading to figure that out. "Sathya Sai Baba said that his followers do not need to give up their original religion, saying 'my objective is the establishment of sanatana dharma, which believes in one God as propitiated by the founders of all religions. So none [sic] has to give up his religion or deity.'" -http://en.wikipedia.org/wiki/Sathya_Sai_Baba#Beliefs_and_practices_of_devotees
According to the same source his followers report that he performed miracles and caused objects to manifest. He also faced criticism based on sexual abuse allegations. It seems that he predicted his own death, but incorrectly. This page (http://www.sathyasai.org/swamihealth/swamiage.htm) goes through a lot of hoop jumping to make it sound like he wasn't wrong. Altogether, sounds like the arch-type of the modern Hindu guru.
This explanation of his teachings is quite lovely and I certainly could not disagree:
Sathya Sai Baba -- His Message http://www.sathyasai.org/intro/message.htm
Sathya Sai Baba encourages us to recognize who we are. We are not these minds. We are not these bodies. We are the eternal spirit that temporarily occupies these minds and bodies. We can appreciate and become who we really are by turning inward with faith in God and an intense yearning to know Him. Our conscience is a reflection of the eternal spirit. Sathya Sai Baba tells us that our conscience is our master. When we follow our conscience, our thoughts, words, and deeds will be noble and consistent. Spirituality is having the courage and determination to follow our conscience in all things and at all times. In doing so, we recognize that we are all united in God. We are bound together by divine love.
I have come to light the lamp of love in your hearts, to see that it shines day by day with added luster. I have come to tell you of this universal, unitary faith, this spiritual principle, this path of love, this duty of love, this obligation to love. Every religion teaches man to fill his being with the glory of God and to evict the pettiness of conceit. It trains him in the methods of unattachment and discernment, so that he may aim high and attain spiritual liberation. Believe that all hearts are motivated by the one and only God; that all faiths glorify the one and only God; that all names in all languages and all forms man can conceive denote the one and only God. His adoration is best done by means of love. Cultivate that attitude of oneness between men of all creeds and all countries. That is the message of love I bring. That is the message I wish you to take to heart. Sathya Sai Baba
Let the different faiths exist, let them flourish, and let the glory of God be sung in all the languages and a variety of tunes. That should be the ideal. Respect the differences between the faiths and recognize them as valid as long as they do not extinguish the flame of unity. Sathya Sai Baba