  We present ``state-of-the-art'' theoretical expressions for the triple
differential B->X_u l^- nu decay rate and for the B->X_s gamma photon spectrum,
which incorporate all known contributions and smoothly interpolate between the
``shape-function region'' of large hadronic energy and small invariant mass,
and the ``OPE region'' in which all hadronic kinematical variables scale with
M_B. The differential rates are given in a form which has no explicit reference
to the mass of the b quark, avoiding the associated uncertainties. Dependence
on m_b enters indirectly through the properties of the leading shape function,
which can be determined by fitting the B->X_s gamma photon spectrum. This
eliminates the dominant theoretical uncertainties from predictions for B->X_u
l^- nu decay distributions, allowing for a precise determination of |V_{ub}|.
In the shape-function region, short-distance and long-distance contributions
are factorized at next-to-leading order in renormalization-group improved
perturbation theory. Higher-order power corrections include effects from
subleading shape functions where they are known. When integrated over
sufficiently large portions in phase space, our results reduce to standard OPE
expressions up to yet unknown O(alpha_s^2) terms. Predictions are presented for
partial B->X_u l^- nu decay rates with various experimental cuts. An elaborate
error analysis is performed that contains all significant theoretical
uncertainties, including weak annihilation effects. We suggest that the latter
can be eliminated by imposing a cut on high lepton invariant mass.
