Ellie and I have been big on groups for the past forty years.
While still in a Methodist parsonage we heard of the small group movement of the Church, called the "group of twelve". It goes back to the days of John Wesley who organized his converts into classes made up of 12 people. They met every week, and among the primary items on the agenda was the question asked of every member "Is it well with your soul today?" (You can be sure that elicited many a heart felt and soul searching confession and resulting dialogue.)
We came to feel that this was the soul of the church. We organized a group of 12 (to which we belonged of course), and no more meaningful activity occurred during our five years at that church. But it caused trouble.
Including 10 people involved excluding an awful lot of others. Some of them were offended. Such is the life of country preachers.
Living in Winston-Salem we were involved in two alternative churches (today they're called emerging churches). Here we found our primary social and spiritual life. They were small groups, the second one aggresively "leaderless" to the degree that was possible. (If there must be a leader, a rotating leadership is the only creative way to go; otherwise you wind up with a guru and disciples. Most people are all too willing to be disciples.)
After ten years there we moved to Washington to be a part of the Church of the Saviour. At that time (in 1973) it consisted of about 160 members organized in about 15 mission groups. The primary life of the church revolved around the activity of the mission groups.
These groups were not exactly leaderless, but sort of...
The church leaders had suggested a form of structure designed to insure that everyone had an active (leadership) role in the group. We had a "prior", responsible for administrative functions, a spiritual director (who received everyone's [usually] written report each week- horrors!), a pastor-prophet (shall we say ranter), and whatever other specialized roles people felt called to. In the groups to which I belonged (over a period of 10 years), I observed virtually no competition for primary roles-- a true blessing.
Moving on, after ten years, we came to Langley Hill Monthly Meeting of the Society of Friends-- an ambitious name for a loosely knit confederation of Quakers who met together once a week (on 'firstday') and sat in silence waiting on the activity of the Holy Spirit. (Home at last!!) There was no visible leader in this activity other than Him. There was a 'riser', who announced the end of the meeting for worship promptly on the hour. And there was a clerk who moderated the business meetings, but generally took no position on any item of discussion.
But this group, as sacred as it became for us, lacked the face to face dialogue and confession that only a small group could provide. That meeting had organized themselves into "Friendly Eights", who met in one of the members' homes for spiritual sharing and sustenance.
Of course there's no such thing as a leaderless activity of any sort. Someone must provide some intiative to get things going. But an essentially leaderless group is possible wherever the convener's ego does not intrude.
In Florida we attended two Quaker meetings. At Ocala a group of 8 to 10 people meet every Sunday, an ideal small group: an hour of worship and an hour of 'meeting for eating' around a large lazy susan where the tone is generally lighter and usually full of levity.
Gainesville is a university town with all sorts of bright people coming to the Quaker meeting there. But once a month for many years they have had a Bible Study--usually 8 or 10. An old gentlemen exercised a form of semi-leadership: we agreed on the book to study for a period of time; then John would bring to the group small portions of the designated chapter, passed around in order. Every person had an opportunity to lead the discussion of the portion he had received. A wonderful leaderless group!
After a while John retired to the West Coast. The meeting named another leader, who was much more directive; some of us lost interest.
The emerging church, as I perceive it, will be made up of small groups such as this. (Actually Harvey Cox had proposed this for the church of the future back in the sixties. Harvey's most important book, called The Secular City, achieved tremendous notoriety and was read by millions, partly because people thought he was writing on the sexual city!)
For a prime example of a virtual leaderless group look at the Friendly Kwakersaur Scripture Study.