Custom variables are name-value pair tags that you can insert in your tracking code in order to refine Google Analytics tracking.
https://developers.google.com/analytics/devguides/collection/gajs/gaTrackingCustomVariables?hl=en
Analytics and Tracking
Get access to data on 22,256 websites Google Analytics Custom Variables Customers. We know of 3,264 live websites using Google Analytics Custom Variables and an additional 18,992 sites that used Google Analytics Custom Variables historically and 743 websites in the United States.
Get a list of 22,256 websites using Google Analytics Custom Variables which includes location information, hosting data, contact details, 3,264 currently live websites and an additional 8,801 domains that redirect to sites in this list. 18,992 sites that used this technology previouslyand 743 websites in the United States currently using Google Analytics Custom Variables.
Countries
Financial
Group
Region