Gatherings of agnostics are, in my experience, just people who meet to talk about the same stuff you see on this thread. It's not at all like a religious gathering, it's more like going out to have coffee with some friends, but not necessarily with coffee. I've heard about non-religious groups in bigger cities where they plan fun things to do together, like day hikes or volunteering for community projects or charity events. It's just a way for people with this one thing in common to get to know each other and feel comfortable in knowing they're not alone. The thing is, agnostics, atheists, free thinkers of all types . . . by their very nature they render groups like this rare and hard to find. They don't have a common belief system that would make grouping together like that necessary, and because they are such free thinkers, their interests, ideas, goals, and thoughts are so varied it's hard to get any sort of collective mind going (which is a good thing, except it has the annoying side effect of making it seem like there are less of us than there actually are). The groups around here are normally short lived, and consist of people getting together once, sharing stories, maybe chatting about favorite movies, making a couple of new friends, and then never coming back again. I don't have a problem with that, because it's not our mutual atheism that bonds me with my atheistic friends. We rarely talk about that stuff at all. No, what bonds us is the activities that we enjoy together, which is exactly what church excels at . . . lumping people together and providing them with a mutual source of interest. BYC does that for chicken addicts. Photography groups do it for camera nuts. Some religious people can get focused on religion being the main source of common interest, so they forget there are a million other activities people form groups about and bond over.
Honestly, for those who have lost their faith and are feeling the loneliness that comes from leaving such a large social network, I wouldn't recommend trying to find groups specifically for agnostics, atheists, non-religious, etc. Instead, think about what you enjoy doing, and try to find groups that center around that. Garden groups, book clubs, jogging groups, hikers, cyclists, sports, volunteer work . . . you get the picture. My fellow atheistic friends were not found through the atheist groups I went to, interestingly enough, but through our other hobbies. I'm just speaking from my experiences, though. You might have a great agnostic based group near you, and if that's the case, yay!