As a freelancer, I often work at companies who use Subversion repositories.
It’d be handy if I could use Mercurial to get code from these repositories, track my changes when I’m offline, and then commit all my local changes to the company’s Subversion server when I’m back online.
Does this work? Have you read any good tutorials on the specifics?
Try HgSubversion. It allows you to do just that. You can clone a (part of) svn repository locally to an hg repository and work with hg locally and svn remotely (push and pull do what you would expect of them).
I have used it with some success in the past but do not have extensive experience with it.