I'm a Christian. The problem I continually run into with people arguing against the existence of God is the "straw man" fallacy, where they caricature God and then proceed to disbelieve in the caricature. The thing is, if you posit for a moment that there is an all-powerful God, then He is, necessarily, bigger than we can comprehend -- He is "outside the box" of reality that we can ever understand. After all, He created the reality that we know, and we will spend forever discovering and refining scientifically our understanding of this reality.
Most people I see who profess atheism seem to fall in three camps:
1) "Brights" -- Dennett, Dawkins, Harris, Hitchens, etc. -- any perception we have of cosmic spirituality or design is really an illusion, in many cases an "accident" of the universe's physical laws playing out over millions or billions of years; this often includes emotions, perceptions of self, and other "human" qualities
2) Angry -- Either something really bad happened to them, where prayers went unanswered, causing them to reject God since He wasn't there for them, or they in general hate authority figures, especially one that they do not see proof for. This is a popular one for the "straw God" argument. My favorite (ahem) is the one where "How could a just and loving God let people suffer (or children die, etc.)?" This ignores a couple of things -- first, that people who suffer may actually go to a cosmic reward that erases all memories of pain; and second (more importantly), it assumes that we can really understand why God does all the things He does. I consider Him transcendent, and beyond human judgment. This does not mean that I don't wonder about certain things. I readily admit that one thing I would really like to know from Him is why pain has to be as bad as it sometimes is. Why is there agony? And before you think I'm just a step away from atheism, stop and try to answer the same question from an evolutionary biology standpoint. What survival purpose does the ability to feel utter incapacitating agony confer that a lower-level "warning" pain does not?
3) Ambivalent people who don't want to commit or don't want to be bothered. Sometimes this is laziness, sometimes it's a wish to not make a direct commitment to one belief in case that bet is wrong. In other words, a sort of "many roads to God" fence-sitting. Sometimes this is expressed as "Christians, Jews, and Muslims are all okay, since they all believe in the same God and are just taking different routes to Him". The problem with this hedging is that the scriptures for each of these religions is pretty clear about its way being the only way, and to fall away to another one is to invite serious spiritual trouble. I grant the 3 of them have a common base, but there are important dogmatic differences that cannot be lightly glossed over.
So, to me, God is a transcendent entity whose manifestation to us limited-understanding humans is that of a loving but sometimes stern and inscrutable Father. When I pray to God, I try very hard not to picture a cartoonish old man with a beard, but more of the incredible expanse of creation surrounding me, with me trying to send a message to its creator. This isn't pantheism -- I'm not saying that the universe is God. I'm trying to say that God created the overwhelming world we all live in, where the level of detail is terrific, and the clockwork nature of how it all works together is dauntingly complex.
Kev