RepositoryNaming
If you are making good use of Mercurial, chances are you will have lots of repositories sitting around.
The reason for this proliferation is that you can easily and cheaply isolate a chunk of work (implementing a new feature, fixing a bug, or whatever) by making a Clone of a Repository.
For myself, it is common to have five to ten repositories sitting around at a time for a single project.
Since each Repository will differ from its siblings in only a few details, giving them meaningful names is important.
I typically use a descriptive name for each one. So hg is my mirror of Matt's tree, hg-gui is my GUI development tree, while hg-export contains my work on the export command.
If you start using a lot of repositories, but do not adhere to a naming convention of some kind, odds are that you will very quickly become confused. On the MailingLists are some threads about repository naming, e.g. repository collection practices.