My Experience
I am an atheist.
When a first got to AA/CA I tried to have an open mind and I worked the steps out of the Big Book with a sponsor. I was sober for 19 months and on step 11 when I relapsed. After four months of drinking and drugging my circumstances were bad enough that I went back to AA/CA and again started working the steps with a sponsor. I relapsed after five months.
My circumstances became even worse and, after losing a number of things, I went to a residential treatment center based on the Minnesota model (i.e.-largely 12 step based) for 30 days. After I finishing an additional month of out-patient treatment in my home town, I decided to stop going to AA/CA.
I certainly believe that there are powers greater than myself, for example, at least half of the people that live in my apartment building. But God, as I understand him, does not exist and there is certainly no higher power to which I can turn over my life and will and to whom I can pray for knowledge of his (or her) will for me and the strength to carry out. Hearing seemingly constant messages to the contrary in AA/CA was not helpful and started to make me feel uneasy.
I do think AA/CA helped me stay sober when I came in the first time. The example of people living life on life's terms without drinking or drugging was very helpful as was the moral support of so many of the members. I do miss the fellowship but, for me at, this time, I find more serenity and peace by not going to AA/CA.