We compare the results of two microrheological experiments on single living cells. In the first one, the creep function J(t) of a cell stretched between two glass plates is measured after applying a constant force step. In the second one, a microbead specifically bound to transmembrane receptors is driven by an oscillating optical trap, and the viscoelastic coefficient G(e)(omega) is retrieved. Both J(t) and G(e)(omega) exhibit power law behaviors: J(t) = A(0)((t)/(t0))(alpha) and vertical bar G(e)(omega)vertical bar = G(0)((omega)/(omega 0))(alpha) with the same exponent alpha approximate to 0.2. This power law behavior is very robust; a is distributed over a narrow range, and shows almost no dependance on the cell type, on the nature of the protein complex which transmits the mechanical stress, nor on the typical length scale of the experiment. On the contrary, the prefactors A(0) and G(0) appear very sensitive to these parameters. Whereas the exponents a are normally distributed over the cell population, the prefactors A(0) and G(0) follow a log-normal repartition.