The right approach depends on your configuration management strategy, which in turn depends on the kind of product you are making. If you are developing a big

The right approach depends on your configuration management strategy, which in turn depends on the kind of product you are making. If you are developing a big system with lots of components that need to work together (e.g. an embedded machine vision system with a multitude of related data-recording, calibration, simulation & test utilities and subsystems), then the matrix showing which versions and configurations are compatible with one-another quickly grows to an unmanageable size. Unless you have a god-like configuration management system, the only practical approach is to go "green trunk" and co-version all of your components. Granted, this doesn't necessarily force you to use a single repo, but a single repo is (at least initially) the simplest approach. Of course, you could go "old-skool" and define interfaces up-front then freeze them, but this just slows your development down to a snail's pace. Better (IMHO) to co-version your components then lean on your integration tests to maintain compatibility.