I would like to see a list of current users of the customer portal.
This is important because I am curious how useful of a feature my subscribers think it is, how good of a job we are doing promoting it, etc
Are you using Chargebee APIs or the web interface to get the list of customers?
If you're using the Web interface, please go to the Subscriptions page and then the Customers tab.
Over here, use the "Filter" option and select the filter option as in the screenshot added below:
This would give you a list of customers who are using the Customer Portal. Please let me know if this works !