A Visual How To (VHT) I worked on has recently been published on MSDN. The VHT, Creating Custom SharePoint Server 2010 Document Sets with Visual Studio 2010 , helps you understand how to create document sets in SharePoint Server 2010 Enterprise Content Management in a declarative way which makes them much more reusable between environments:
Document sets, introduced in Microsoft SharePoint Server 2010, enable users to create a composite item that consists of properties and child documents. This enables customers to associate multiple documents with a single work item and wrap them into a single version or workflow. The SharePoint browser-based user interface (UI) makes it easy to create document sets. However, developers may want to create document sets by using Microsoft Visual Studio 2010 and package them in portable and reusable solution packages (.wsp files). This Visual How To demonstrates how to create a custom document set by using the SharePoint development tools in Microsoft Visual Studio 2010.