ghosteye85: The only notice I ever received that there was even a sale going on was about 3 hours after it ended.
GOG actually sent 3 e-mails. The first was when the sale started (e-mail subject "Collect XP to unlock free games with deals up to -90%! The Monstrous Fall Sale is here!"), one when games were added to GOG Connect (e-mail subject "Fall Sale: 20 new games on GOG Connect & 350+ deals up to -90%") and one when the final deals were added (e-mail subject "Fall Sale Ending Soon: last chance for hundreds of deals up to -90%"). If you've only gotten the last one, check your spam folder (as already mentioned), but if the only one you received was the first one after the sale ended, do send a support ticket.
And be aware that you can always follow the RSS feed instead of the e-mails, for faster notifications.