I guess it depends on how the discs are warped.
If they have gone "wobbly" (wich is almost always the way it goes), then it you can definately feel uneven braking when coasting very slowly and applying the brakes softly. Sometimes the pedal may feel spongy and you might also feel feedback, almost as if the ABS is working, particularly at low speed. If this is the case, generally most of the pad contacts the disc at some point in the roation of the wheel though. Braking force is reduced and it becomes difficult to accurately modulate the brakes, and skimming is certainly recommended.
On the other hand (in theory), if the disks have somehow become either concave or convex, it might more accurately describe the symptoms. You will not feel a wobble as described above, and new pads will not seat correctly. One will seat on the outer edge, the other on the inner. Brakes will feel spongy as in reality you are flexing the calipers to align with the discs. However, once the pads are worn in, the symptoms will dissappear.
I have however never actually seen a disc warped like this, and don't know if it can really happen. Kinda doubt it, but I am not prepared to put anything on a block.
Also note that a caliper mounted skew (due to dirt under the mounting points or similar) would produce exactly the same results and is far more likely to happen...