If I had my way, I would dub any church that grew by (say) 20% a "hero church," no matter its size, or if it gave its "fair share" to the UUA. One more stipulation: it would have to get certified each year. No fair "growing" by not submitting statistics each year.
That said, with 515 congregations reporting, there were twenty-six hero churches. Most are small - the largest is the Overland Park, Kansas Shawnee Mission Unitarian Universalist Church growing from 187 to 232, a 24.1% growth.
Small or not, their cumulative growth of 474 members (from a group of 2,290 members in 2004) is half of the net growth in all certified churches.
Three are in Kansas (Overland Park, Topeka, and Lawrence) and North Carolina (New Bern, the greatest percentage grower, Hillsborough, and Brevard) each. California, Michigan, Oregon, and Virginia each have two.
I don't see obvious links between them. (I do know the young-ish ministers in a few, but since my knowledge of ministers skews young, that's hardly scientific.)
If there are traits these congregations have in common, it would be a great help to all the rest.