From the Introduction:
Curses are magical twists of fate that horrify and enlighten. Unlike a fireball directed purely by will, a curse is backed by the authority of .... well, something. The horsemen of the Qo Sho Nu nation call curses the spears of destiny, cast down by the Horse Mother to avenge. The blind mystics of the walled city of Orin say that it is merely a dreadful symmetry. And if the DM has chosen the right way to bring them in curses should be fun for the players and miserable for the characters. After all, although the DM isn’t the enemy of the players it is his job to screw with the characters, frustrate them and occasionally kill them. These spells are not replacements for the Bestow Curse / Remove Curse combination given in Core Rulebook I. These are completely new spells and can be thought of as extended options for flavor and seeds for ideas. These curses are standard spells but oriented towards the brutal and obscure.