One of the relatively new features in PHP 5.2, is the DateTime class/functions. It has a few useful functions (date_parse, date_date_set, date_time_set etc) which make dealing with dates and times easier (date_parse provides some useful error info too).

He also mentions the ability of the functionality to handles dates before 1970 or after 2038, a common problem with PHP's native date functionality. He illustrates how it's useful by describing the change they made in Propel store DateTime objects instead of the integer timestamps like before.