Several user reports are available that allow you to determine overall user activity, sorted by various criteria.
The user reports list:

This report shows the activity of customers and shop visitors and their total page views for the selected date range. The statistic is sorted by total views.
This report shows overall statistics for orders grouped by customer. The data shown includes subtotal, tax, shipping, discount, and total amounts.
Only orders with the payment status RECEIVED and the order status COMPLETED will be shown for the set period.
This report shows statistics for discount and user groups, sorted by customer. The data shown includes the group names, the discounts and expiration dates.
This report shows statistics about the current reward point balance of all customers. The data shown includes the earliest reward points date, the latest expiration date and the current reward points balance of each customer, sorted by name
This reports shows statistics about all user reward point transactions for a set date range, sorted by date. The data shown includes, the internal reward point id, the customer’s user ID, the type of the reward points transaction, the order ID, if present, the start and expiration date (if applicable) and the reward points of the transaction.