This paper contains both theoretical results and experimental data on the
behavior of the dimensions of the cohomology spaces H^1(G,E_n), where Gamma is
a lattice in SL(2,C) and E_n is one of the standard self-dual modules. In the
case Gamma = SL(2,O) for the ring of integers O in an imaginary quadratic
number field, we make the theory of lifting explicit and obtain lower bounds
linear in n. We have accumulated a large amount of experimental data in this
case, as well as for some geometrically constructed and mostly non-arithmetic
groups. The computations for SL(2,O) lead us to discover two instances with
non-lifted classes in the cohomology. We also derive an upper bound of size
O(n^2 / log n) for any fixed lattice Gamma in the general case. We discuss a
number of new questions and conjectures suggested by our results and our
experimental data.