We have 50 standard products/services but we need to capture specific information about that product or service configuration for each account. For example, we provide hosted FirstClass software for 100 customers, and we have to record on which of 10 servers we installed that customer. 

I created a custom field (pick list) on the Product for Server Number, but when I update it for one customer, it changes for all customers using that product.

How do I capture the unique configurations so tech support can work effectively with a customer?