Experience Bonuses are bonuses to Experience that the player receives when doing specific tasks, Much like achievements. However, it is not known if they act like Achievements and/or Statistics. They were first seen in the GamesCom 2009 demo.
Experience Bonuses give the player experience for accomplishing certain tasks, such as the "Massacre" Exp. Bonus, which award player Exp. based on the number of monsters he killed in a row. The Gamescom 2009 demo videos, showed the player receiving 75 xp for killing 20 monsters in a row, while another showed the player receiving 24 xp for killing 11 monsters in a row, on top of the xp earned for killing the monsters independently.
It can be assumed, that killing monsters as fast as possible is more beneficial to the player.
It can also be assumed that there are many types of Exp. Bonuses, other than "Massacre". For Example, the 1Up 1Up