VMware has shown a great deal of commitment by publishing an official (yet experimental) guide to creating VI Client plugins.
“With the release of VirtualCenter 2.5, VMware offers third-party developers and partners the ability to extend the VMware Infrastructure Client (VI Client) with their own product-specific menu selections or toolbar icons that provide access to external, Web-based functionality. These extensions, or VI Client Plug-ins, comprise the set of configuration files, URLs, icons, and Web-server-hosted resources that work together to display extended menu items, icons, and other user interface (UI) items in the VI Client and provide access to the external functionality.”
In related news, Andrew Kutz (who also posted his thoughts about the guide and how it relates his own unofficial guide) is publishing a book with O’Reilly on “Programming and Managing VMware Infrastructure“.