For a detailed review of this subject I refer to a recent paper
\cite{Voloshin:2008dg}; in this talk I only very briefly comment on a few most
important questions: (a) Very recent significant progress in viscous
hydrodynamics calculations (b) Initial eccentricity/flow fluctuations, the
effect of which has been clarified recently (c) Initial conditions, in
particular the role of the gradients in the initial velocity field, (d)
Puzzling system size dependence of directed flow (e) Azimuthal correlations
that are sensitive to the strong parity violation (f) Future measurements at
RHIC and LHC, including pp-collisionsComment: 6 pages. Proceedings. Invited talk at PANIC 2008 conference, Eilat,
Israel, November 200