My DOAP (Description of a Project) vocabulary has been one of those slow-burning projects. A gentle increase in interest, followed by plenty of pleasant discoveries of where its been deployed.
What I feel to be one of the best considered and implemented deployments of DOAP has been launched on the Apache Software Foundation projects site. Apache are using DOAP as part of a project to describe and map out the vast array of projects that are part of the foundation's activities.
In addition to the DOAP vocabulary as specified by me, Apache have added an extension to describe which standards a project implements. They've done this in a well-documented and non-intrusive way. Also, the categories mechanism has been used in just the way I envisaged, allowing a convenient navigation of Apache actitivies. The tips for authors on how to put together the DOAP file are also a great resource.
Reading around the site, it looks like having a DOAP file in place for each project will also reap big adminstration benefits for the foundation. I look forward with interest to seeing how this grows. I'm really impressed with the quality of the implementation.