According to Beliefnet, more than one fifth of Americans self-identify with the label "spiritual but not religious," which I've always interpreted as "religious but lazy." Stepping back and viewing the phrase in a slightly less judgmental tone, it is more than likely an attempt to distance oneself from the dreaded term "organized religion;" a personal declaration of "I'm not one of them." But, as we atheists have long ago realized, it's not the act of organizing that's bad, it's the unfounded beliefs. "Oh I'll keep the irrationality, thank you. I just don't want to be organized."
As I've become aware of this mass diaspora of coordination, I began to realize than I'm, in fact, surrounded by people with completely indefinable beliefs. Many of them find it difficult to even verbalize things that they feel strongly about. The most entertaining way I've had someone describe their belief system to me was with a wrist twisting motion; as in, "I believe in (holds hand next to head, flicks wrist a bit)". At first, I thought that he had become distracted by a fly, but once I realized that the little wrist twitch was intended as a description of his religious beliefs, my heart sank a bit.