At the beginning of this century, Razumov and Stroganov have noticed that the wavefunction of the ground state of the XXZ spin chain at Delta=-1/2 (a physical system whose study has a long history), displays several enumerations related to different classes of Alternating Sign Matrices (ASM) and more generically has a rich combinatorial structure. After recalling some of the main conjectures of R-S, we show how to exploit the relation between the solution of the level 1 U_q(\hat{sl_2})} qKZ equation and the ground state of the inhomogeneous XXZ spin chain at Delta=-1/2 in order to compute the exact Emptiness Formation Probability (EFP) of a periodic chain of finite length. The EFP turns out to have a nice factorized form and in certain cases reduces to enumerations of ASM or of certain symmetry classes of Plane Partitions.