A friend has 3 mountain laurel bushes in Zone 5b which he planted in the fall of 2009. All three are suffering from the same affliction: within about 3 weeks time between May 23rd and June 11th, they went from looking fabulous and healthy - about to bloom -- to the leaves turning uniformly brown and the bush looking terrible! He was out of town, but a local nursery claims there was some cold weather during this time. Otherwise, they couldn't help us diagnose the problem.
Here is a picture of the front side of a leaf:
