Integrating trunk revisions with forked Hg project

How do I fork a continually-evolving project to customise for a specific client, while continually pulling improvements from the major branch without losing my customisations?

Should I just keep pulling from the main repository, merging appropriate changes and never push back?

I haven't been using Mercurial long, so I am concerned about integrating the two projects without making a mess of changed namespaces and different domain (client) logic.

Update: It looks like using separate repositories which pull from a main repository is the way to go.

The way you're using it:

Should I just keep pulling from the main repository, merging appropriate changes and never push back?

is precisely my preferred way of handling this. Any change that applies to multiple customers gets done in the main repo and pulled into the per-customer repos. Any per-customer changes are done in the per-customer repo and never pushed back to main.

We use named branches. Make a branch from the default with the customizations and merge the changes from the default into the named branch as needed.