I am not a nymph fisherman. I have caught fish on nymphs but my success has been sporadic. It's just going to take MUCH more practice.
Having said that, one of my first fish caught on a nymph was last summer when water levels were low and the water was warm. I had floated a female parachute adams through a pool several time with the same trout swimming lazily up, inspecting it and then going back down to the bottom of the pool. In desperation, I tied on a nymph dropper and the first time back through the same pool, the same trout took the nymph. It was a very visible, slow motion kind of demonstration on the benefit of being able to fish with nymphs. As a general practice, I still prefer fishing dries only but learning to fish with nymphs when they're needed is a must for me. If you can routinely fish the double rig, as danp413 said, it gives the fish both options in the same cast.
Although I much prefer dries, I bought some BHPT yesterday so I still intend to keep plugging on the nymphs.
His eye is on the sparrow and I know He watches me.