Knob and Tube Wiring
Knob and tube wiring was one of the first methods of running electrical power in a house. It served its purpose well for many years but its exposed installation and age makes it a safety issue. Home insurance companies often require it to be replaced before they will insure a house. It's a lot like tires, even if they've been great for years (and even if they've just been sitting there doing nothing), they deteriorate and need to be replaced.
We're quite experienced with this work and we've produced great results. Since our typical work involves snaking wires in homes, we are good at refeeding the knob-and-tube lights, switches and outlets without disturbing the walls and ceilings.
Of course, some homes are easier than others but with a planned approach with the goal of minimizing holes, etc., the finished product is quite nice.
We start by doing an evaluation of the house and what is affected by the knob-and-tube wiring. But even with good planning, there can be surprises so it helps to be flexible.
In one house, as we did the one main circuit, we discovered patchwork wiring hidden under the attic insulation that was being fed with modern wiring. Unfortunately, that made more work but it had to done.
This link takes you to a good article decribing knob and tube wiring in greater detail.