This research was started and partially conducted during the Schloss Dagstuhl seminar 12101 on “Computation and Incentives in Social Choice”. We are grateful to the organizers of this seminar (Edith Elkind, Christian Klamler, Jeffrey Rosenschein, M. Remzi Sanver) and to the Dagstuhl staff for providing a stimulating atmosphere. Robert Bredereck is supported by the DFG, research project PAWS, NI 369/10. Jiehua Chen is supported by the Studienstiftung des Deutschen Volkes. Gerhard Woeginger acknowledges support by the Netherlands Organization for Scientific Research (NWO), Grant 639.033.403, and by DIAMANT (an NWO mathematics cluster).