  Precision tests of the CKM mechanism and searches for new physics in the
flavour sector require dedicated QCD calculations of decay widths and spectra.
Significant progress has been achieved in recent years in computing inclusive B
decay spectra into light energetic partons. I briefly review different
theoretical approaches to this problem focusing on the determination of
|V_{ub}| from inclusive semileptonic decays and show that this determination is
robust. The largest uncertainty is associated with the value of the b quark
mass. Finally I present new numerical results in the DGE resummation-based
approach, now including O(beta_0 alpha_s^2) corrections. The results are
presented for all relevant experimental cuts, from which a preliminary average
is derived: |V_{ub}| = (4.30 \pm 0.16 (exp) ^{+0.09}_{-0.13} (th)
^{+0.39}_{-0.34} (m_b)) 10^{-3}, where the PDG value of the b quark mass,
m_b^{\MSbar} = 4.20 \pm 0.07 GeV, is assumed.
