Every list seems to go through the same cycle:

1.  Initial enthusiasm (people introduce themselves, and gush a lot about
    how wonderful it is to find kindred souls).

2.  Evangelism (people moan about how few folks are posting to the list,
     and brainstorm recruitment strategies).

3.  Growth (more and more people join, more and more lengthy threads
     develop, occasional off-topic threads pop up).

4.  Community (lots of threads, some more relevant than others; lots of
     information and advice is exchanged; experts help other experts as
     well as less experienced colleagues; friendships develop; people tease
     each other; newcomers are welcomed with generosity and patience;
     everyone -- newbie and expert alike -- feels comfortable asking
     questions, suggesting answers, and sharing opinions).

5.  Discomfort with diversity (the number of messages increases
     dramatically; not every thread is fascinating to every reader; people
     start complaining about the signal-to-noise ratio; person 1 threatens
     to quit if *other* people don't limit discussion to person 1's pet
     topic; person 2 agrees with person 1; person 3 tells 1 & 2 to lighten
     up; more bandwidth is wasted complaining about off-topic threads than
     is used for the threads themselves; everyone gets annoyed).

6a. Smug complacency and stagnation (the purists flame everyone who asks
     an 'old' question or responds with humor to a serious post; newbies
     are rebuffed; traffic drops to a doze-producing level of a few minor
     issues; all interesting discussions happen by private email and are
     limited to a few participants; the purists spend lots of time
     self-righteously congratulating each other on keeping off-topic
     threads off the list).

OR

6b. Maturity (a few people quit in a huff; the rest of the participants
     stay near stage 4, with stage 5 popping up briefly every few weeks;
     many people wear out their second or third 'delete' key, but the list
     lives contentedly ever after).

Posted in many places, including here.