For the talk I knocked together a very simple demo plugin, which extracts data from the MongoDB system.profiles collection providing details of recent Mongo queries. This is available on github. At some point soon, I will fix it up properly.
There is also a fanstatic guide to writing Glimpse plugins from, Anthony van der Hoorn one of the authors of Glimpse on their blog. Part 1 will get you stated, and Part 2 shows the real value of writing custom plugins targetted at your code, helping you provide rich diagnostics for your web application, and keeping your code nice and clean. Well worth checking them out.