Setting the Bounds of the "Local" Church

What exactly is a "local" church? Do we have a tendency to read "local" in the NT when we should be seeing universal? More importantly, perhaps, what constitutes a local church? Organization? Membership? Covenant?

The question has many implications. There are implications for the legitimacy of the emergent church movement. There are further implications for the administering of baptism and the Lord's Table.

I know this is a HUGE question to ask (much less answer) in a blog post. So let me narrow it down a bit for now. In what sense can 5 guys who love God passionately get together at McDonald's and be called a church? We certainly don't doubt that they are members of the Church (capital "C"), but do they now constitute a "local" church? More specifically, could they break out their "grape product" (Dr. Windsor's term) and bread and have communion?

I think the ramifications of this discussion are even more enormous than I understand at this point, but I would love some input anyway.