Let it be known to all nations, kindreds, tongues, and people, this will read like a polemic, but it is not intended to be (overly) offensive. Unable to share my thoughts with anyone on issues that I have surrounding the church of my youth, I have resorted to talking to myself on the internet. Heaven have mercy...
Am I a Son Of Perdition? Most, except those closest to me, would argue no. Have I committed the unpardonable sin of denying the Holy Ghost? An iniquity more egregious than any combination of sex and or violence conceivable (not even virtuoso evil pricks like Stalin, Hitler, or even George Bush have achieved this level of depravity). Not yet. In the mormon cosmological model, there is a special place reserved for these SOPs, the only true and living version of hell ominously called Outer Darkness.
To qualify you have to of course deny Mr. fancy pants look-at-me-I-can-turn-into-a-dove himself. Can you feel the spirit brother? It's a Holy Ghost party up in here. Umm, yeah, the Holy Ghost there's no denying him, but to even attempt such a rash and despicable act you have to first know that the mormon church is true. Joseph Smith described this as looking at the sun (which might make you blind), and denying that it shines, or crucifying the good Lord once again, even while knowing he's the chosen Messiah. That's what it comes down to, you have a sure knowledge that Jesus is Jesus and then you go all Judas Iscariot, on his godly ass. That'll get you a one way ticket to mormon hell my friend.
Now, it's generally accepted that you have to really know, like Generally Authority know*, that the Church is true with absolute certainty to even have the opportunity to become a SOP. Like Jesus has to take a time out from his busy schedule of basking in the eternal worship of his angel sycophants, descend from his throne of glory, and confirm that your calling and election has been made sure by personally delivering your VIP pass to the celestial kingdom, while the Holy Ghost sears a powerful witness of these events into your very soul. It's no easy feat getting into outer darkness let me tell you. You've got to be worthy of heaven, if you want to go to hell.
Most of us fail to attain the aforementioned level of knowing, by which I mean really knowing. For the rank and file members (and probably the overseeing patriarchy as well, although they'd probably never openly admit it) testimony baring is a culturally acceptable form of consolation; a statement professing knowledge of the truthfulness of God, Jesus, the church, Joseph Smith etc. It's the old fake it till you make it gambit, which isn't a bad thing in and of itself. It's a perfectly acceptable form of learning. The question is how many actually make it? You know, gain a sure knowledge of the truth, enough to make them eligible to be condemned to Outer Darkness if they ever fall? Ask any honest mormon and they'll tell you not many if any. Am I a SOP? Hell, no. I only ever believed the church was true, even though I said I knew as much (possibly like everyone else? Hello, emperor, nice clothes you've got there). Belief 0r faith is not the equivalent of certainty, of that I am certain.
*General Authority n. Old mormon guy who resides in the upper echelon of the mormon hierarchy. I'm giving them the benefit of the doubt here, but Boyd K. Packer has hinted that a GAs testimony is no different than a standard members.