The Network Plugin Auditor lets you track which plugins were used on which sites. It adds columns to your network admin to show which sites are using each plugin, saving you the trouble of having to visit every dashboard to find out.
Would be great to test this little baby out to help us during our upgrades: http://wordpress.org/extend/plugins/network-plugin-auditor/
Multisite Plugin Stats is similar: This is a simple plugin that shows plugin activations across all your sites. It is particularly useful for checking to see which plugins are not being used at all so that you can deactivate those as needed. You can also find out which are the most popularly used plugins on your network.
Download Multisite Plugin Stats here: http://wordpress.org/extend/plugins/multisite-plugin-stats/
One Comment
We have had another one in the past to do something like this but web.unc.edu has grown too large to do this with a plugin. These plugins look at the options table of every site to generate these plugin stats. With 2000 sites it is just too big and the PHP script times out.
I did just test both of these. The first one only seems to work about 1/2 of the time. It does not work at all on the plugin pages. It shows at least 1 site with activated plugins on the right hand side of sites listing, but that is not really that helpful.
The second one times out like the other plugin statistics plugins.
I have almost completed a php script that we can edit to pull this info out when we need it. In addition to pulling how many people are using a particular theme/plugin we can pull the site ID’s, as well as the administrator email addresses so we can email them if we need to upgrade a plugin or theme.