A colleague and I were talking about the what should go in his production kit next. He suggested a Sennheiser 416 shotgun microphone, to which I replied that he should really get a wireless lav kit. The reason being is that he's a one man band corporate video guy and doesn't have a sound mixer with him. Shotgun mics really need to be used in an echo-free environment with the little or no background noise. A lavalier microphone isolates a speaker from the background and doesn't require a sound mixer to follow the speaker with the boom pole.
Two weeks ago I was at NAB and recorded a number of interviews for Video Gear. I had my friend's suggested combo: Channel 1 = lav, Channel 2 = shotgun microphone thinking the same thing he was. I would try to use the shotgun a backup if something went wrong with the lav, because wireless audio isn't perfect either. Below is a short video with the results
As you can hear, the shotgun microphone audio was pretty much worthless at 6 feet from the subject. Now this isn't to say that a shotgun microphone is worthless. It just says that there are optimal tools for different situations. If I would have had a sound mixer with a boom pole we could have gotten really good results by placing the shotgun microphone much closer. The lavaliere microphone already has this advantage because it's pinned to his collar.
My guess is that my friend will pickup a used wireless lav kit off Ebay and be much better off.