Based on developer feedback as well as our own goals of making the end to end story for VSX developers easier, we have created a new web page on the VSX Developer Center site for a more simple, quick, and easy process of obtaining PLKs and SLKs.
Below is a link to the new page (and there are links to it on the http://msdn.com/vsx home page). Copied below the link is the description of PLKs and SLKs.
Package Load Keys (PLK) and Shell Load Keys (SLK) are required for your VSPackages and Visual Studio Shell applications to load successfully. The form below allows you generate the PLK or SLK needed for your VSPackages and Visual Studio Shell applications to load successfully. If you agree to the terms defined in the Visual Studio SDK you used to develop your Visual Studio Package or Visual Studio Shell application, then you can use this form to generate the appropriate load key.
Package Load Keys (PLK)
To prevent unauthenticated VSPackages from running in Visual Studio, each VSPackage to be loaded in a deployed application must have a valid PLK. The Visual Studio SDK provides a Developer Load Key (DLK) that makes it possible for VSPackages to load without a PLK during development.
Shell Load Keys (SLK)
Each isolated Visual Studio Shell based application to be deployed must have a valid SLK. The SLK is uniquely related to the application and cannot be used to open any other application.