Introduce a new class to support the PHP DateTime class to support local timezones, etc. Handling date/time using this class would significantly improve the handling of date/time in both the core and across all modules. Creating a unified class would also allow us to handle date/time as an object.
Obviously the core would have to provide an upgrade path to convert user/server timezone settings to be in line with the DateTime class (e.g. 'America/Chicago' instead of '(GMT-6:00) Central Time (US & Canada), Mexico City').