I think Facebook has gotten bad press for privacy issues, but for the average user, changes in interface seem to cause the most anguish. I am an active user of eBay and when they are rolling out a new interface, there is a period when the user can toggle between the new and old formats. I think a little forewarning may head off some of the heat generated when there is a format change. Likewise, having an easy to find help page, explaining the layout of a new interface would be a wonderful asset to the system.