I'm (kind of) one of them. Long story, and I've told it so many times in so many places that I apologize if you've already read this elsewhere in the Forums.
I grew up in a Bible Methodist / Wesleyan Holiness background. Bible Methodism isn't properly classified as Pentecostal, but it became a launchpad for my engagement with Pentecostal/Charismatic theology because of their similarities. (For instance, both groups teach a second, perfectionistic work of grace, and both favor letting the Holy Spirit lead the worship in the charismatic sense.) Basically, I had a crisis of faith after reading a short story written by a theistic evolutionist, and I reacted by plunging deeper into the more charismatic side of Holiness teaching, which in turn led me to explore the teachings of a Third Wave house church movement localized in Britain, which in turn led me to explore the teachings of Hobart Freeman--the writings of whom were introduced to me by a girl I was looking to start dating at the time. I was never a Pentecostal in the sense of joining a Pentecostal congregation, but doctrinally I was one.
Ironically, both the house church movement and Dr. Freeman had taught sovereign election in theory (though Freeman frequently contradicted it in his sermons), so when I finally became disenchanted with both groups' charismatic doctrines, I took a tentative look at Calvinism. Most of my subsequent conversion to Reformed Presbyterianism consisted of dismantling Freeman's beliefs in successive stages. It occurred in an order that is more or less opposite of what I hear is the common order: I accepted progressive sanctification first, the Real Presence in Communion second, the inherent goodness of Creation (i.e., acceptance of medicine's use and alcohol's consumption) third, persistence of the saints fourth, the catholicity of the Church and Vossian amillenialism fifth, the cessation of the charismata sixth--this marked the end of my "cage stage", mainly because the girl I mentioned earlier finally got sick of debating with me about theological issues that she didn't really understand--particular atonement seventh, infant baptism eighth, dichotomist anthropology (as opposed to trichotomy) ninth, and justifying faith as fiducia (rather than Free Grace's mere mental assent) tenth.
So yeah. I was Vossian before I was five-Pointer. Weird, huh?