I thought it was especially engineers who believe in God - and creation in particular - apparently they are prone to see "design" in everything. On the other hand, scientists who work in a science field related to evolution theory almost all reject creation; 99.86% in a poll about 20 years ago in the USA (country with relatively many creationists).
Generally though, a smaller percentage of scientists believe in God than the population of a country as a whole. I suspect this is because they have to critically examine alot of things, without bias, and as such it becomes easier to see the flaws in the 'arguments' for God, and there is little to no (peer) pressure on them to be impressed by those arguments
Are some of us atheists because:
...
3. Because we have a rebelious nature, and atheism is just a "rebel's religion"?
This is exactly the reason why I chose not to believe - my parents were (are) Christians, though they don't practise their religion alot, and during puberty I wanted to disassociate myself from them a little. Not that I called myself an atheist, actually I considered myself agnostic for years and thought atheists were foolish, claiming to know there is no God, until I was repeatedly explained (by Stegocephalian among others) that agnosticism and atheism overlap..
However I grew out of that rebellious nature and now I reject the idea of a God simply because there is no credible evidence.
And I would also say there would be no atheists if there wouldn't be theists, people who claim there is a God, in the first place - it is merely a response on our part.
But yeah I think it is an important point that atheists tend to be rebels or outcasts. This is probably because in most areas/countries one religion or another dominates (christianity, islam) and a dominating religion brings alot of connections, identity, values etc. to them, so those who do not have much of a connection with their society tend to reject the dominating religion more often.

. But no, the worms have eaten him, 
That's a very interesting point Conrad and ofcourse one that's impossible to answer. I dare say that for some aetheists, there is some kind of psycological motivation that comprises some part of the foundation of their belief.
However, I would say with near certainty that, for an aetheist, there was some kind of psycological (possibly emotional), motivation involved in their undertaking of aetheism, even if it does not exist (no pun intended) after the point where one describes him/her self as an aetheist.