In my anthropology classes back in the dark ages "Organized Religion" had a very specific meaning: It was any religion where Ritual and a Priesthood trained in the Ritual controlled access to the God or Gods. these types of religions are also those with written dogma.
Unorganized Religions are those where a Shaman or "Medicine Man" or some individual has received a vision or calling and has direct access to the Gods. These are sometimes called "Primitive Religions" but some of them are anything but primitive. Here in modern America, we appear to have a mix of this in our religious practices. The Christian sects that see their leaders as the only "Right" conduits to God such as those who followed Jim Jones are examples.
Sociologists and anthropologists have suggested that all religions started out unorganized and as they expanded they developed a priesthood and rules of worship. If you read the bible as a historic document you can see some of this kind of development.
Most religious schisms have been over ritual and church politics, as in the Moslem Sunni - Shiaa split. Occasionally there is a basic difference over fundamental dogmatic belief as in the Protestant revolt in 1517. The role of Faith played a big part there.
Jesus of Nazareth probably saw himself as a reformer of what he (and other devout Jews of his time) perceived as a religion that had become too influenced by the Romans, was too corrupt, and had forgotten its true role and way.
The religious leaders (all those Sadducees and Pharisees) undoubtedly saw him as a threat and had enough pull with the Roman procurator to have him executed as a common criminal. The rise of his followers was probably because he gave them a hope which was lacking in most of the other religions of the time - that of a much better life after death. He inspired Faith in only a few followers but they managed to inspire Faith in many many more during the next several hundred years and in the process the Christian religion became very much an "Organized" religion.

I dissagree with Creed_of_Kings. If anything, a person claiming to be a "postmodernist" would most likely belong to one of the "Mainstream" religious denominations, most of which are prime examples of "Organized" Religion. A postmodernist who considered himself a liberal might reject the point of view of a "Fundimentalist" sect, but even though most of these are organized, they seem more likely nowadays to have some kind of "Charismatic Leader" who dictates both religious and political dogma to his flock under the guise of "Morality". This is more a characteristic of "unorganized" than "organized" religion.
To be sure, many people currently decry religious intrusion into politics or attempts by religious groups to impost their moral order on non-members. Right now, in Ohio, for example, there is a bill before the legislature to outlaw ALL abortions and make transportion of anyone across state lines to receive an abortion, a felony. This bill is clearly a violation of Ohioan's constitutional rights as they are currently intrepreted, and an attempt to impose a particular moral rule on everyone.

Blacksox has come up with an interesting point of semantics. In English we use the word "Faith" to mean unquestioned belief, or belief unsupported by factual evidence, which are two quite different things. For example we have faith that the sun will rise because it always has - we have lots of physical evidence. We believe in God because our culture has, from our childhood, taught us to. That being said, the human emotional need for security seems to predicate belief in something "Bigger" than we are as a human psychological given. Humans tend to have faith in SOMETHING, no matter how Atheistic they claim to be.
The difference between organized an unorganized religion is, of course, blurred in practice. I would say Wiccan and other neopagan religions are good examples of unorganized religion. Covens pretty much depend on a charismatic leader who tends to adjust the ritual to suit her/himself. Even well-organized groups like the Golden Dawn tend to do this.