The Content Organizer is a new site-level feature of SharePoint 2010 that allows you to route a document from a drop-off library to a custom location based upon that document's metadata.

Document Sets are implemented as a new site collection-level feature (because turning the feature on deploys a new content type called "Document Set") of SharePoint 2010 that allows you to treat multiple documents as one collective unit; all documents share the same metadata, can be involved in the same workflow at the same time, are versioned together, etc.

Using the two together, I noticed an interesting issue:  my Document Sets were not being routed properly by the Content Organizer.  After doing some research, I found this helpful blog post at "From The Field" that explains exactly what was missing:  the Document ID Service site collection-level feature.

For some reason, you must enable the Document ID Service site collection-level feature to allow the Content Organizer to route Document Sets.  SharePoint, as always, is an interesting creature.  The more we use it, the more interesting things we notice.