I guess different rules apply in SaaS-land. At least Salesforce.com warns its customers before it goes dark; I saw this notice when I logged in this morning.
Friday March 09, 09:00 PM EST
Saturday March 10, 05:00 AM EST
Please be advised that salesforce.com will be performing scheduled maintenance during the above time period.
Salesforce will not be available during this period. Please plan accordingly. We apologize for any inconvenience to you and your business.