I recently had a conversation with a colleague of mine who was saying that lapel micing is the preferred choice of recording dialogue on set over boom micing. His argument was based on an article he had read from Skywalker Sound where the industry pros there prefer the sound of a lapel over the sound of a boom mic.
In my experience, I have always worked with industry pros who will use lapels, but only as a last resort and prefer the sound of a boom mic. I agree with this because of the natural quality of the boom mic (shotgun, supercardiod etc) and the fact that you can control it in concert with the level of dialogue delivery verses the acoustics of the location. In some instances, I have gone with a lapel and a boom but this decision is based entirely on the blocking of the scene and the size of the shot (generally medium wide with 2 to 3 actors moving in the scene.) The lapel mic, for me, no matter where it is placed, still sounds a little boxy and you cannot follow like you can with a boom. The natural harmony of warm dialogue with the space around the actors is much more present with a boom than it is with a lapel.
I would be interested in hearing your ideas on the matter.