Here is a very handy module that lets you do the impossible! Being a Magento shop owner/admin have you ever wanted to login as one of your customers to see how the customer portal interface, order details etc looked like? Normally such a login is impossible unless you ask your customer for the password or you yourself reset it.
This module when installed will add Login As Buttons/links in the customer details and customer list admin interface. All it takes to login as a customer is to click this button or link.
See the Module in Action