I would say the biggest change is that the default SQL mode will be the equivalent to 5.6's ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION,ERROR_

I would say the biggest change is that the default SQL mode will be the equivalent to 5.6's ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION,ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE,NO_ZERO_IN_DATE,NO_AUTO_CREATE_USER. This means that a number of statements that produced warnings (but proceeded) will now produce errors. I have some slides on it here: http://www.slideshare.net/morgo/upcoming-changes-in-mysql-57 http://www.slideshare.net/morgo/upcoming-changes-in-mysql-57 (see slide 33 onwards).