With DVCS you can create your own branch and push it to other systems super easily, so there's little excuse for checking in broken code to a shared branch. Also, with a lot of newer VCSes there's often a feature to "shelve" a changeset to a central DB without committing it.
Not to mention that breaking the build for more than a few minutes raises some serious red flags about the way you're working.
But there are a few cases where it's a necessary evil. For example, when upgrading a large Rails application from Rails 2.3 to 3.0, you're likely to make hundreds of small changes before everything works again.
In this case, I create a new branch, prepend "BROKEN:" to each commit message, and record the number of unit tests that are currently passing. Once all the tests are fixed, I hand-test, add new tests for any regressions that weren't caught by the automatic tests, and merge back to the main development branch.
Only if no one else ever saw that part of history, right?
:: shaky eyes ::