You know what's interesting? When I first started pointing out that Calvinism is essentially a redux of Gnosticism it was entirely due to my own observations; I had never heard anybody say anything like that previously. I was reading St. Irenaeus of Lyon's Against Heresies at the time and as I went on I realized more and more that what he was describing about the Gnostics matches exactly the beliefs of Calvinists, sometimes even with the same terminology. Since that "discovery," though, I've been surprised by the great amount of people I've come across who have reached the exact same conclusion independently. Even Bishop Julian of Eclanum, one of St. Augustine's chief opponents within his own lifetime, noted that Augustine seemed to be carrying a lot of Gnostic baggage into his Christianity.
Whenever I raise this point to Calvinists, their only defense seems to be to deny Gnostic terminology. "The elect aren't saved by nature as the Gnostics say; the elect are saved by grace." Terminology aside, Calvinists and Gnostics are saying the exact same thing; the Gnostics are just being more honest about it. The elect are born to be saved and so, for all practical purposes, are born saved irregardless of anything they may or may not do (just as the non-elect are born damned irregardless of anything they may or may not do). You don't have to say it's part of your "nature" to be saved, but if salvation is something that you are born into or born to do -- it's part of your nature, simple as that. The Gnostics said it was because of the "divine spark," and the Calvinists say it's because of "grace." Different terminology, same soteriology.
I want to recommend that everyone take a listen to this excellent audio lecture by Dr. Jeffrey Macdonald (an expert in early Christian history and a member of my former parish) in which he discusses St. Augustine's unique theology and the overwhelming influence it has had on the West, both Roman Catholic and Protestant. He also briefly touches on the Gnostic influence that led Augustine to some of his erroneous conclusions. The most interesting aspect, for me, is the look that Dr. Macdonald takes at the reaction amongst other Christian Fathers, such as Ss. John Cassian and Vincent of Lerins, to Augustine's theology.
By the way, his whole series of lectures is great. Apparently, he gave them at the parish he attends (and I used to attend and hope to get back to once the Army days are over), St. John the Forerunner Orthodox Church in Cedar Park, Texas; I wasn't around when he gave any of them, though, so they're all new (and very exciting) to me.