What does the underside of the leaf look like? Stippling of the upper leaf surface can be the result of lacebugs feeding on the under surface, but it's difficult to tell if this is the case from the picture. Your County Extension Service or a good local nursery should be able to diagnose the problem.

Maingrower is right on. The speckles are symtoms that something is happening on the underside of the leaf. Here are some possibilities:

1) Rust: Small bright yellow spots is a symptom of Azalea (and rhododendron) Rust, Puccininastrum vaccinii, a fungal disease. Orange-red pustules containing spores form on the lower surface of the leaf. This rust is only sporadically severe and typically infects deciduous azaleas. Control by avoiding those hybrids and species which are very susceptible to rust. Good air circulation is helpful. Triadimefon seems to help, but may not be registered for use on rhododendrons.

2) Lace Bugs: Whitish specks on the upper surface of leaves and dark spots varnish-like on the bottom are symptoms of Rhododendron Lace Bugs, Stephanitis rhododendri, and Azalea Lace Bugs, Stephanitis pyrioides, small insects with transparent wings on under-surface of leaves. This insect hatches early in spring as the new foliage begins to mature and its numbers may build to damaging levels with successive generations. Lace bugs reach their peak in late summer and do their worst in sunny, exposed sites. Spiders are important predators of lace bugs and since they shy away from sunny, hot places, plant your azaleas where there is some shade. Insecticidal soap, horticultural oil, or a systemic insecticide may spare your azaleas the damage if applied in spring when the first hatchlings are noticed. Care must be taken to spray the lower surfaces of the leaves where the lace bugs live. Moving a plant to an area with more shade may alleviate the problem. Lace bugs are more prevalent on certain varieties.

Here is a link that might be useful: Rhododendron and Azalea Problems

spider mites.
2 cents:)