You know, I've gone back and forth on the whole trinity doctrine thing. I'm not really sure where I stand on it except that if the trinity doctrine is 'true', it's not taught as a concept (as such) explicitly in scripture but rather, trinity is implied at some level. The trinity doctrine itself has problems, but I can't really tell if that's just because it's a feeble attempt of finite man at describing an infinite God, or if it really is contrary to what scripture teaches. I've seen good arguments on both sides. It seems that with respect to "trinity" itself (irrespective of the holes in the actual doctrine), it does at least seem implied by the personhood of The Father, The Son, and the Holy Spirit. The tetchy thing about Unitarianism for me is that from what I've seen, it runs dangerously close to if it does not actually deny, either the personhood or the deity of "part" of the One God that seems clearly identified as God somewhere in scripture. We at least know that God is in some sense a "plural" entity, because of the language used by God at creation: "Let usmake man in ourimage."
But that's sort of the crux of the problem in the debate between the two. It seems to ultimately boil down to an argument of semantics if you have either a Unitarian or a Trinitarian view that identifies the Father, Son and Holy Spirit as separate in some sense or lumps two or more of them together. I can't seem to really settle on either view.