Good thread, some nice disscussion going on here! I really liked those vid clips too, those skaters must have been totally freaked out when that guy didnt back down and then started dropping them. he didnt seem to have good "technique" but he had a good attitude and he looked pretty strong and mad so that must be what did it for him. The old guy looked like he irim=tsuki'd (spelling) those guys in the face which must have been effective cos they were jumping at him.
Randori/ji-yu-waza whatever you call at, is standard dojo practise for a multiple attack situation and can be done in a variety of ways.
In a "real fight" though, the best thing to do is to follow the above advice. If your backed into a tight corner, start screaming, look mad, shout random things and cover your balls.
Best way to dispose of someone quickly is to break their nose. So aim for the nose. Dont pin anybody. If your lucky enough to put someone down and they have friends coming and/or look like they are going to get up and come at you again then kick them. Just be careful you dont seriously injure them and that there arent any cctv cameras around, the courts tend to take a dim view of kicking someone on the floor, even if there is several attackers and they started it.
Always fight dirty
Edit: Dont forget the old disclaimer of: "It was all a blur officer, they jumped me and i just tried to push them off and get away and then I think one of them fell down or something. He must have tripped. I dont really remember much else..."