one problem with infrared is that a camera flash can trigger them as well--in fact, if the sensor is sensitive enough, even a change in room lighting will set them off. I use wein IR stuff in the studio where I work, and have done some events work with it as well--but mostly use pocket wizards for that. The IR stuff can be set off in a dark room (the wein, anyways, it's very sensitive) if you flip the room lights on. In fact, last week we had a speedo pack that was firing at random almost with a wein IR slave in it--it was picking up a flickering fluorescent light about 50 feet away....
The radio slaves are the way to go.I use pocket wizards for my own stuff, and they're great. I actually bring them into work to use for events, because the wein IR stuff is too finicky--and if anyone else is shooting, you can't use IR.....
The nikon stuff---I used that SU4 slave and used the SB26 system as well--for shooting events. One guy would use a strobe on a pole as the main or fill, and the shooter would use a flash on camera to trigger it. Depending on the ratios, you'd be filling from the camera, or using the second light to light up the background etc. We used to do this on manual actually, because all the automatic stuff, even the SU4 is too buggy. You get into line of sight problems with the sensors. Radio slaves are great for this work though. You can put a strobe behind a wall and trigger it. You can stick them outside and fire through windows, you can isolate channels and set up lights for different zones, etc.
the IR triggers, are just little on camera flashes with a neutral density gel almost. in a pinch, you can just use the slaves and use a little strobe to trigger them. They work great in a controlled area, not so great if anyone else is around shooting with strobe. OTOH--I used to perversely get a kick out of this.We'd light a stage area with strobes to shoot some function, and someone in the audience would try to take a shot with a point & shoot and all this speedotron stuff would go off....it'd be annoying really, but then again, you knew that exposure was just toast.