From LennethEX's post on the shoryuken forums:

About 2 weeks ago I started tracking down how and where 3S stored the hitboxes using MAME. Well a few days ago I made some progress and using the MAME renderer I'm now able to draw the hitboxes to the screen while the game is running.

Here is a small test video:

http://www.youtube.com/watch?v=KimKJCjfPFs

It's not perfect yet and there a display issues with vertical screen scrolling but it seems to work pretty well.

More later.

I have to say I'm pretty blown away by this. I've seen diagrams made before on a single frame, but dynamic real time hit box overlay could be an invaluable training tool for fighting game players. I can't wait to see more of this!