It is harder because there is no central figure point like theists religions have. I feel that unity is important for me but I have met many atheists who don't feel it as important. I joined my local atheist group, the atheist community of austin.
http://www.atheist-community.org/
I made great friends there. I have networked with other atheists via the net just for friendship and found it to be fullfilling. I have only been an atheist less than one year. I could write for quite a while in things I have learned and seen in the secular world and how others have come to atheism or dealt with converting from theism.
It has helped me quite a bit. Both in coming to terms of a world without God and more importantly seeing others interact in a theists populated enviroment as an atheist.
As to are they united, It seems that in the USA (which is the only country I have read about with atheism), atheist are moving towards unity with free thought clubs, atheist clubs and secular groups. I see the rift it creates in the theist community by seeing groups who don't believe in god form and I hope over time it isn't seen as a hostile engagement but as a way for non-theists to group and bond just as any other group will and does.
