Since no one has answered this question yet... I thought I'd start the discussion. Others please chime in.

Although I don't feel that there is a "perfect" size for a church, I also don't feel that we should ever be satisfied with the size of the church. (If I were able to use italics, the words "a" and "the" would be emphasized). In other words, while the size of one particular church can vary in its size and ministry style, The Church should always be growing. I hope that our little church would reflect the growing body of Christ.

In a semi-related thought, because humans have needs (refer to Maslow about this) for security, safety and relationship, there is such thing as "critical mass."  I remember back to when I was the leader of a middle school youth group; 3/4 of our kids graduated up to 8th grade, but there were only 2 younger kids moving up to replace them. The group shrunk to about 8 students on a good night, and continued to shrink because they missed the fellowship and comfort in anonymity that other students provided for them. For a few months we merged the middle schoolers with the high schoolers, just enough time for them to feel comfortable, start bringing friends and then when the leaders saw that "critical mass" was reached we split the groups again.  So I guess I would add a secondary question to continue the conversation: "Is the "perfect" size about personal comfort or expanding ministry?"