Here we have a video of the El Fuerte infinite that has been discussed all over the place at this point. Game breaking? Who knows. Will it be patched? Who cares, just dont get caught in it!
Apparently the way to do it it cancel your fierce into the run, and cancel the run into another fierce. So the actual break down is..
Standing close fierce punch, qcf+p (initiates run), lp (stops the run), standing close fierce punch.
Repeat until dizzy! Have fun!