  We study perturbation of holographic dark energy and find it be stable. We
study the fate of the universe when interacting holographic dark energy is
present, and discuss a simple phenomenological classification of the
interacting holographic dark energy models. We also discuss the cosmic
coincidence problem in the context of holographic dark energy. We find that the
coincidence problem can not be completely solved by adding an interacting term.
Inflation may provide a better solution of the coincidence problem.
