launching part of a site

Say I want to launch part of a site that only has a couple parts of the
site active (so, a couple controllers would be active and the rest
would not be). What would be the best way of doing that? Creating a
branch in subversion for the partial launch? And then as I do updates,
merge the changes back and forth between the trunk and the branch?

A branch is not a bad idea.

Alternatively, you could just customize your routes to only route
requests to the controllers you want visible... and get rid of the
generic routes like:

map.connect ':controller/:action/:id'


Branching is the best idea, though if you want something quick and dirty you could simply make all your controller methods protected.