Here is a patch which adds the date format "dd/mm/yyyy" to Core/Form/Date.php and Utils/Date.php, so that Import can support that date format. The date format is rather common in Canada and Europe.
Note: unlike the other regexes, it only matches '/^\d\d[-\/]\d\d[-\/]\d\d\d\d/' without the ending '$'. This is because the data we are importing has the date and time in the field (ex: "26/04/2007 15:31"). I think that the Import functions should tolerate this
Patch was generated using the SVN trunk. Tested in CiviCRM 1.8 PHP5.
Mathieu Lutfy (bgm on freenode)