Yes, it is bad. I've seen some of the central FL groves that are decimated.
Last weekend on NPR I heard an interview with a citrus greening researcher who said some HLB resistant trees have been identified in Florida, India, China and other locations where greening is widespread. They are being biochemically evaluated and genetically tested to identify the source(s) of this resistance. Hopefully these trees can be used as stock for future planting/breeding. When asked how serious greening is, he said something like 'if citrus canker is like a having a cold then greening is like having cancer'.