  As is well known, $B^0_{d,s}$--$\bar B^0_{d,s}$ mixing offers a profound
probe into the effects of physics beyond the Standard Model. The data obtained
at the $e^+e^-$ $B$ factories have already provided valuable insights into the
$B_d$-meson system, and very recently also the $B^0_s$--$\bar B^0_s$
oscillation frequency $\Delta M_s$ has been measured at the Tevatron. We give a
critical discussion of the interpretation of these data in terms of
model-independent new-physics parameters. We address in particular the impact
of the uncertainties of the relevant input parameters, set benchmarks for their
accuracies as required by future precision measurements at the LHC, and explore
the prospects for new CP-violating effects in the $B_s$ system. To complement
our model-independent analysis, we also discuss the constraints imposed by the
CDF measurement of $\Delta M_s$ on popular models of new physics, namely
scenarios with an extra $Z'$ boson and supersymmetry. We find that the new data
still leave sizeable room for new-physics contributions to $B^0_{s}$--$\bar
B^0_{s}$ mixing, which could be detected at the LHC.
