We know that LV cales can't pass through or be concealed in walls per Article 411. The aggravation that some of these installations pose, along with trying to explain to homeowners why you can't use LV cable, makes me wonder why someone doesn't get a UL listing for a LV cable that can be concealed. It would eliminate the "junction/transition" fittings, and probably make the job go much smoother.
The 2005 code will allow cables feeding low voltage lights to be concealed if the power supply is a listed class 2 power supply and the cable is also listed as a class 2 cable. Due to the power source limitations (see table 11(A) in Chapter 9), this may not be practical for some installations.
Few things are harder to put up with than the annoyance of a good example.