Remote-Learner gave me the okay to post their plugin usage statistics using percentages. I have attached the results here.
The first page (the chart) shows the percentage of sites in the sample using third party (non-core) plugins in each plugin category, as well as the percentage of unique plugins within each category being used. The site percentages are based on polling a sample of Moodle sites - somewhere between 800 and 1000. The percentage of unique plugins in each plugin category is based on the total of all unique plugins in all categories - over 1000.
The remaining pages show the most popular plugins within each category, by percentage of total sites polled. The percentage in use refers to plugins that have been installed on the site, and are actually being used in courses (where this is meaningful), while the percentage enabled refers to plugins that are installed and enabled.
It is interesting to see the similarities in data.