Well, I'm not exactly an atheist, more of an agnostic (but atheistic to a lot of god concepts, including the ever popular bible one).
The reason I more or less lack belief in god is precisely because I realized I could not really proove his existence. I realized that I don't usually give "the benefit of the doubt" to other concepts that have not been proven (tooth fairy), so why should I do the same for YHWH or any potential deity? I think also that a lot of people, in addition to thinking they have logical proofs of god, have some sort of "spiritual connection" to their "heavenly father". For me, however, god was always primarily an intellectual connection, and not an emotional one. Sure I felt some "love" for him, and appreciated all he supposedly did for me, but this was mainly premised by the fact that I thought there was really solid evidence for his existence. Indirect stuff like "look at all those pretty and orderly stars up there, a god must exist!" never did it for me. Due to a lack of education on the subject, I believed that what I was taught about the bible was true. We really were created 6,000 years ago just as the bible says, with mounds of proof to back it up, I thought. There's great extra biblical documenation of what Jesus did as described in the bible, I thought. All those prophecies that have been claimed to be fortold and fullfilled by the bible really did come to pass, I thought. With such a sureness of mind on whether God existed (and all the colorings of the "problem of evil" and other things about god's nature that I accepted), it was easy for me to worship god.
Once I realized all these things weren't true, and that things like the "problem of evil" don't logically disappear by passing the buck to us humans, there was nothing left there for me. I couldn't pull myself to believe in something's existence that I had no real evidence for. If and when a god clearly and objectively reveals itself (god would know what it takes to do this, being all knowing and all ), then I'll believe for sure, untill then I suspend judgement. But somehow I do suspect that even if a goddess does exist, she really wouldn't care if we worshipped her anyway, and assuming she's rational, she'd understand why.