  Using updated measurements and SU(3)-breaking form factors, we have a
detailed look at the B_d -> pi^+ pi^-, B_s -> K^+ K^- and B_d -> pi^\mp K^\pm,
B_s -> pi^\pm K^\mp systems. The corresponding decays are related to each other
by the U-spin symmetry of strong interactions and offer determinations of the
angle gamma of the unitarity triangle. In the former case, we obtain
gamma=(68.3^{+4.8}_{-5.7}^{+5.0}_{-3.7}) deg, which is in excellent agreement
with the Standard-Model fits of the unitarity triangle. The first errors
correspond to experimental input uncertainties, while the latter are an
estimate of U-spin-breaking effects. In view of this result, large CP-violating
new-physics effects at the amplitude level are excluded. However, the effective
B_s -> K^+ K^- lifetime and the mixing-induced CP violation in this channel
offer interesting probes for New Physics in B^0_s-\bar B^0_s mixing. In the
case of the B_d -> \pi^\mp K^\pm, B_s -> pi^\pm K^\mp system, using additional
information from B^\pm -> \pi^\pm K, we obtain a bound of gamma \leq
(71.8^{+5.4}_{-4.3}) deg, and the range 24 deg \leq gamma \leq 71 deg. We
perform also tests of the U-spin symmetry and do not find any indication for
large non-factorizable corrections.
