On the View User window, go to the Statistics tab and you will see a "last logged out" value. You asked about last logged "in" value, but the last logged "out" value should equally allow you to find people who don't use the product. Unfortunately, there is no "last logged out" column on the Users list window, which could have allowed you to sort on the column and easily group the users who are least active. However, what you can do is bring up the View User window, switch to the Statistics tab, and arrow through the user records looking for older "last logged out" values. That will take you a little bit of time if you have a high user count, but it is possible to get the data.