(see CategoryHowTo for a list of all HOWTO pages)
Usage models:
WorkingPractices describing several ways to use Mercurial
How to handle MultipleCommitters
CommunicatingChanges describes the various ways Mercurial can exchange changesets
How SymbolicLinks work
RepositoryCorruption describes how to deal with repository and dirstate corruption
Setup and Automation:
PublishingRepositories describes various ways to make your code visible to the world
MercurialOnSourceforge explains how to serve Mercurial repositories using Sourceforge.
Features:
NamedBranches gives an introduction to this feature
See also: FAQ, TipsAndTricks