There may be many similarities (can't think of a bunch right now) between theists and atheists, but similarities aren't the point. The important point is the differences between atheists and theists: Most atheists value critical thinking, skepticism, demands of proof for extraordinary claims and constantly being on the lookout for errors in one's epistemology. Most important is a willingness to change one's beliefs when new facts and information are presented, something rarely seen among theists...
Regarding atheist organizations and conferences, people aren't usually congregating
for something, they're
against something: against religious dogma's influence in political decisions, against creationism being taught in public schools, against religions' unfair tax exemptions, against persecution of atheists from the government and the general public, etc.. Atheists are a diverse bunch; we are individually
for different things, but collectively
against the same things...
P.S. Hep, don't take it personally: we not only disbelieve in your god, but all gods