It is the gathering of friends, family and community that is the most beneficial aspect of a church, and that really has very little to do with "gods" and "worship".
Not the ones I've gone to- at my Churches, we tend to talk about God, sing about God, etc. It's different at picnics or potlucks the Churches have on occasion and we don't call those "going to Church"- even if it is at the building (which it usually isn't). The building itself isn't the Church- it's the body of believers.
Anyway, this is about calling an atheist gathering a "Church". I don't care what they call it, but the word "Church" is usually used for people practicing and preaching about God, religious faith, etc.