A systematic study of magnetic dipole strength in the even-even Gd-148-160 nuclei and over the much larger region of heavy rare-earth nuclei is carried out. Within a quasiparticle description for the Nilsson model, all possible two-quasiparticle K-pi = 1+ states are constructed and thus, calculating the corresponding B(M1) reduced transition probabilities, information on the total summed magnetic dipole strength and on its fragmentation is obtained. We get as our main results that most of the M1 excitation strength comes from two-quasiparticle (2qp) excitations, with states up to E(x) less-than-or-equal-to 4 MeV being mainly orbital in nature. The higher energy region 4 MeV < E(x) less-than-or-equal-to 9 MeV is characterized mainly by spin-flip M1 strength. The results are compared with existing experimental (e, e'), (gamma, gamma') and (p, p') data and one nucleon transfer results for Dy-164. Some general features are discussed.