I leave it totally open ended… Whether you’ve used them or know something cool about them… fire away!!!!(I though it would be interesting to start something like this, especially to help beginner learn and more advanced users to recap on some of the wonderful features of SharePoint that would otherwise not get the attention).
They are a great to use to implement Transmittals. A transmittal is the controlled distribution of formal documents to engineers, sub-contractors, vendors, fabricators, government bodies and other parties in the form of a cover page identifying the information that is included in the contractual documents being delivered.
I once had to essentially build the document set features for Moss 2007 for a project for London Underground.
If document sets had been available it would have saved us some time 🙂