  The X-ray observation of black hole candidates provides a valuable tool to
probe regions very close to the central black hole, where strong-field
relativistic effects become important. Recent studies have shown that these
effects seem to manifest themselves in the observed X-ray spectrum, in terms of
the shape of X-ray continuum and the profile of emission lines, and in the
X-ray light curves, in terms of certain quasi-periodic oscillations (QPOs). The
latter will be the focus of this paper. We will review the proposed
observational evidence for gravitomagnetic precession in black hole candidates,
in light of new observational data and alternative models. Quantitative
comparison will be made between the data and the models. We will comment on
recent theoretical and observational efforts to address whether the
gravitomagnetic precession of accreted, orbiting matter around a rotating black
hole is a viable process for producing the observed QPOs. The results are
inconclusive. We will mention a few areas where further progress can be made to
possibly shed more light on the issue.
