Apart from that, this poll has its own little curious points. - Not only does atheism seem to undermine your moral authority, but also being a Muslim, or being homosexual, being a woman or black too, to lesser degree. All of these seem to be 'defects' for the common electorate that a potential canditate would have to compensate for.
As to the OP:
1 - How it is to be an atheist?
It's a non-issue. I'm an atheist, but I don't define myself by it.
2 - Have you ever gotten in a less favorable situation because of it?
3 - Are you open about about it?
Sure. If someone asks me about it, I'll give them an honest answer.
4 - Do your family and co-workers know it?
My family is familiar and fine with my world view. As to co-workers, this is something I would not discuss there, simply because I don't see why it would be relevant.