About a couple of months ago we migrated Aspose.Words development from Subversion to Mercurial. To setup and learn and document new procedures was a bit steep, but the productivity and morale has soared. We never looked back.
We have several projects. Just Aspose.Words for .NET consists of 600K+ lines of code, it is in one repository and we have 20-30 feature branches as well as some special branches active at the same time. Switching, merging and code reviews are fast and easy. If you are considering whether to switch to a DVCS, my advice - just do it. It is almost like thinking about have source control or not at all.
This is a screenshot of the Aspose.Words repository. It might look like an overly busy train station with a lot of opportunities to train wreck. Bun in reality it works very smoothly and logical. It almost looks after itself.