as a non-christian I've never felt comfortable around churches or church people, once I had to do some campaigning for an issue I wanted the county to pass, and had to go to every community leader in the county, and pretty much because of that almost every church in a large city... some churches were very warm and welcoming and didnt care at all that I wasnt a christian (well... the Episcopalian church anyway. They and their openly lesbian minister were very welcoming, heck they had a "church dog" that ran arround the pews getting petted... If I was going to renounce my atheism, and my eastern philosophical bends, I'd probably become episcopalian just because they were about the nicest people I met doing this) others though treated me like a criminal infiltrator and plague victem when after they asked if I was a christian I told them and didnt lie.
I'd say if your not a christian and you want to go to a church to socialize (weird but ok) find out about the church before you go, and IMOHO avoid anything evangellical or charismatic...