Both my daughter's bike and her husband's bike have disc brakes; I rode hers brand-new from the LBS and while it braked great, I didn't experience the wet-my-pants "OMG the brakes are so friggin' good" sensation. But then, perhaps I have a high tolerance for crappy brakes: having ridden a bunch of less-than-stellar motorcycles over the years, nowadays my criteria is "will the thing slow down if I apply brakes hard enough"

As an engineer though, and having worked on accelerating and decelerating (braking) machinery which is driven by many hundreds of horsepower, the subject of braking can be very fascinating--especially when the human element is involved. Human-initiated braking systems are usually not linear, partly by the inherent design of the mechanism, and partly by intent. Human muscle groups don't work linearly and human perception isn't linear. Some braking systems take this into account; for example, how about a car's brake pedal, activated by the foot. Let's say the pedal travels 10 cm total with a force of 100 lbs (I hate to mix metric units with imperial but it fits better here). If the brake system was perfectly linear, a brake pedal of travel of 1 cm (10%) would require 10 lbs of force and exert 10% of the maximum braking capability. A brake pedal travel of 2 cm (20%) would require 20 lbs of actuation force and yield 20% of the maximum braking capacity, etc. That first 10% might be perceived as being too "grabby" in a passenger luxury sedan so perhaps the designer may tone it back a little, perhaps through the design of the actuating mechanism or through a "snubber" in the brake line. In a sports car though having a little more braking force on initial application may be perceived as a good thing, the driver may think the brakes are more "snappy" and the designer may tweak the system accordingly.

For a bike disc brake system, it's actuated by the hand lever, which pushes on a piston in the master cylinder. This piston displaces hydraulic fluid and generates pressure in the hydraulic system. The hydraulic pressure in turn moves a larger piston, and thus yields a mechanical advantage (small master cylinder piston, large slave cylinder piston). The braking force from a given hydraulic fluid pressure is actually fairly linear: if 500 psi is full braking torque on the wheel, then 50 psi would be about 10% braking torque on the wheel. However, the hand lever's interaction on the hydraulic fluid's pressure isn't linear: the lever is moving about a pivot, pushing on the piston at different angles, and is thus non-linear. Also, the hand's squeeze force is likely non-linear as well. So if the brake lever moves 30 mm at 30 lbs of hand squeeze to achieve full brake lock-up, a 10 mm lever movement probably won't be 10 lbs and probably won't be 1/3 of full braking torque. However, it might be perceived as operating quite linearly because of the human body's perception of force! (That's perfectly acceptable,by the way).

A rim brake also operates non-linearly: the lever's pull on the cable isn't perfectly linear, the cable's actuation of the brake mechanism won't be exactly linear either. We could carefully plot the geometry of the system at various braking points and determine how non-linear it is. I could certainly envision how a very perceptive driver could feel the difference in non-linearity between a rim system and a disc system, even though both systems could be quite capable of achieving the same wheel lock-up at the same amount of brake lever squeeze. So if a rider prefers a disc brake feel, great; if a rider doesn't notice, that's okay too.