I've always had a very short refractory period, sometimes it has been nil ... i.e. the erection persists after coming. There's nothing that fires me up so much as staying hard, still inside, and very possibly swelling up just a little beyond the norm. As Benderten says, these second bouts often involve the most monstrous erections.

More typically however, the return to normal is very gradual. The post orgasmic state is very different in appearance and sensation from a normal 'semi' though, at least it is in my case.