The lessons offered by Usenet are relearned by just about every online forum, usually in the most painful manner possible. This sequence of events, repeated often enough to be called an archetype, runs as follows. With awareness, care, and enough willing, the forum can renew and refresh, cycling through the middle stages indefinitely.
The Beginning, when there were only a few people, and everyone cared and things didn't quite work the way they were supposed to and the inner workings of the software was clear and comprehensible. The unwritten rules and meta-rules make their first appearance, often mirroring the attitudes and personalities of the founders.
The Golden Age, when you could always count on interesting interchanges, most of the personalities are familiar but there are enough new faces for things to be interesting. During this phase the software achieves a relatively stable form, the unwritten rules are written down so that they need not be explained and re-explained, it's a period of growth and discovery.
The Decline, the formation of cliques and factions, incidents of abuse, of intellectual violence and namecalling. The software becomes encrusted with patches and extensions, the unwritten rules are flouted regularly and the meta-rules all but forgotten. It is a time of either shrinking membership, or overwhelming growth.
The Fall, an incident, whether social or technical that makes everybody realize that things aren't like they used to be. It usually leads to a revision or addition to the software as this is the easiest thing to fix.
The Present which is either a Golden Age or the Decline Of Everything Decent and Good, depending on whom you ask.
The Diaspora (suggested by PeterMerel) Is the process of people moving on to found new CommUnities or join others, often spreading mannerisms and ideas from one forum to the broader set that is the InterNet.
For a longer discussion on this, see:
Online communities often experience similar problems within similar contexts. Often the solutions to these problems are alike.See also:
I am mindful of the CommunityLifeCycle now that it has been defined. It is still inevitable? I believe in CommunitySolution. See also CommunityMayNotScale. -- SunirShah
CIX (CompulinkInformationExchange?) has been in its golden age for over 10 years. -- DaveHarris
If you were to take out software-specific references, the CommunityLifeCycle could easily be a history of almost every kind of subculture known to man. Which makes me wonder if there's a place in the life cycle to insert the input of broader mainstream exposure, and dilution of original ideas & social mores. Probably The Fall, I suppose.
One subculture where "The Fall" however doesn't tend to happen is pub culture - in a UK context at least - a large number of pubs are several hundred years old, and in many respects the social aspects of various online communities have similarities - the people flowing in and out change but the character stays essentially the same, some people hang around forever, and others just pop in whilst on a crawl. The most long-lived online communities seem to have greater similarities to pubs than some other communities.