Quantum spin-1/2 antiferromagnet on a triangular lattice is a textbook example of frustrated magnet.  Its phase diagram in a magnetic field consists of several co-planar spin phases. It also includes a collinear up-up-down (uud) state at 1/3 of the full magnetization M. In my talk I focus on the fate of this interesting commensurate state in a system with spatially anisotropic exchange interactions between spins, as appropriate for experimental realizations of current interest: Cs_2CuCl_4, Cs_2CuBr_4 and LiVCuO_4. I argue that in such Heisenberg model the magnetization plateau at M=1/3 is present for all values of the spatial anisotropy.