One site I support recently had a calendar problem. We were using the Event module from Drupal, although Date has made improvements so that it could be used today. Events were posted on the calendar that corresponded with the organization's most important external events. They maintained an internal schedule of all rooms and meetings using a Microsoft Access tool that had been developed by a former employee, and it could not accept a date beyond December 31, 2009. (Can you say Y2K plus 10?)
