Final comments on fascinating properties of dark energy and some open questions about its nature.
A. S. thanks the participants of Gravity Probe B Theory Group for discussing his talk on Kepler problem with dark energy. A. Ch. thanks I. D. Karachentsev, N. V. Emelyanov, and G. S. Bisnovatyi-Kogan for their collaboration and fruitful discussions. We are grateful to Kseniya Makarova for her help in preparing figures.