The Open Packaging Conventions (OPC) are an open standard for packaging content. The .NET Framework 3.0 provides an OPC implementation (See System.IO.Packaging), and WPF utilizes OPC (eg Pack URIs for identifying and loading "content").

This MSDN Magazine article, by Jack Davis and Andrey Shur of Microsoft, provides a good introduction to OPC and how you can (and when you should) use this technology to solve a variety of interesting problems. Recommended.