You'll notice that a lot of "login" based websites have a Keep me logged in
checkbox which if checked, creates a cookie that stores your password info for that site. Facebook is an ar$e like that as it randomly checks the box and you have to manually un-check it (which I do).
There are browser settings which can prevent the saving of passwords... Internet Explorer 8+
(Tools, Internet Options) General Tab General Tab - Delete History Content Tab Content Tab - Set AutoComplete settings
Setting these options (check/un-check) will allow for you to configure IE to not save
your username & password details.