I just noticed a session at the Nonprofit Software Developers Summit that is probably happening right now.
Marnie Webb is facilitating. Here's the description (notes here?)
The NPTech tag is used on del.icio.us and Tehcnorati to designate technical resources that may be useful to nonprofits. It started right when these sites had just started, and it arose from the need to develop a nonprofit technology taxonomy. The idea was to tell people to tag with nptech everything that is relevant and then look to see what was being tagged to see how the tags were being used. It was a big surprise that this started being used by a large group of people, and also that tags started being used for just about everything (photos, blog posts, etc.).
nptech was chosen so that it made sense, and because it was short -- short and intuitive. Therefore, the goal was to encourage people to use it. Over time, as people started using it more often, it was being used to market and advertise. At first, tagging (bookmarking) was used for individual use, and then it started being more social and more as a means to broadcast information.
The problem with seeing how it was used is that there wasn't necessarily enough data about how people were tagging -- as in there was not enough sites that multiple people tagged Also,del.icio.us is not easy to get a large amount of data out of.
In evaluating the use of the nptech tag, it was discovered that a lot of people were using the tag, but not necessarily reading the tag. It was also discovered that people want a directory of resources.