it depends on the resolution and the resolution of the render-target.
using 800x600 and a render-target 512x512 is not as fast as without this effect, but playable on my 3ghz radeon9800;) the fps goes down pi mal daumen around the half but its still playable
it should be tested however in every case.

if it gets too slow, you can rewrite it to 10passes for example and thus it gets much faster but less smooth

if its used for flythrus or inbetween sequences the fps doesnt realy matter in my opinion

anyone used it and got it to work?