I have the Verizon version and just did a couple of videos, one with Antishake on and one with it off. Though the difference was not great, I could definitely tell there was less shake with the Antishake turned on. So while it's not as effective as OIS or IBIS on digital cameras (far from it), it's definitely working to some degree on my phone.
However, I am experiencing a bit of stuttering during movie playback that I did not notice until just now. For example, the two videos I shot: when I play them back, it will jump around a bit (not shake, but actual dropping of frames). Not sure if something is going on in the background or what, but I'll have to experiment a bit more.