Usage models:
WorkingPractices describing several somewhat sane ways to use Mercurial
How to handle MultipleCommitters
CommunicatingChanges describes the various ways Mercurial can exchange changesets
Setup and Automation:
PublishingRepositories and ServerInstall describes various ways to make your code visible to the world
MercurialOnSourceforge explains how to serve Mercurial repositories using Sourceforge.
NamedBranches gives an introduction to this recent feature