Well, mostly you don't need to care. I don't think there's a real situation where you would need to know their password. If anyone else knows different, please let us know.
If they forget their password, you just delete that account, and give them a new one; takes seconds. You can use the Enable Account step to test the vality of an account (returns an error if the account isn't there); you cannot "test" their password however.
If you need to test a Privilege Set you can create dummy accounts for yourself, so you can log in as different privileges to test access. You don't need to use any person's account.
You can prevent them however, if you want. It is a checkbox there when you create/edit a Privilege Set.
Thanks, I guess I was being a little controlling...:-) good to get simple answer...
now on to graphs and charts...