Our A320s are equipped with this "Thrust Bump" function.
It is activated by 2 guarded pushbuttons located on the thrust levers and according to our manuals gives about 10% improvement in thrust.
But as mcdhu says, it is very detrimental for engine life and we only use it in the cases where takeoff using the normal engine rating would not be possible. And we make an entry in the tech log when we use it.
The improvement on the perfo MTOW is about 2 Tons with bump.
Hope this will help...