Member of what?

In light of this poll on MorethanDodgeBall and the NCLS Survey that our church took part in yesterday, I've been wandering about what church (and specifically youth ministry) desires people to be a part of and if we are really successful.

I know, we want all people, not just teens, to put their faith in Christ. This is what the bible says and what we tell people. This is the aim.

BUT...
Do we actually create members of denominations or churches?
Do we actually create members of specific congregations?
Do we actually create members of niche specific groups?

The questions arise when I see teens "pop out the top" of the youth ministry cycle and then disappear. Where they actually "converted" to the youth group, not something more permanent?

Is the same thing reflected when, for whatever reason, a service shuts down (or is merged with another) and people vanish?

Is a similar thing displayed when someone moves and a church of their denomination isn't nearby, so they stop attending church altogether?