Um, I close the browser from time to time and even reboot the PC at least once a week, but I've only had to log into the forums here twice in the last year...  I've never "logged off."

At home, my desktop & laptop always remember my login credentials for all my favourite forums.
 
Running Firefox Portable is different - every new session wants full credentials for all sites.
 
This is a conscious decision of mine since the firm I [currently] work for are still using an outdated IE version, which doesn't play well with forum software.

Perhaps I should note that I never post from anywhere except my home PC (which is also my "office" PC).  I don't use either my tablet or my nice new Samsung Galaxy Note 3 smartphone with forums.