  After reviewing several mechanisms proposed to get a dS/Minkowski vacuum in
moduli stabilization scenarios of type-IIB superstring orientifold
compactifications we propose a criterium for characterizing those that may
effectively lead to a positive small cosmological constant.
  We suggest that the variation in the expectation value of a good uplifting
term, due to the shift in the minimum of the potential after uplifting, is much
smaller than the original cosmological constant. This is studied with some
detail in Large volume scenarios where the dependency on the volume direction
is rather generic and easy to spot. Here we find that an uplifting term in the
potential, with generic form $V_{up}\sim 1/{\cal V}^\gamma$, should be
restricted to the one satisfying $\gamma^2\ll 12$.
  Such a bound might explain why in models previously studied no uplifting has
been achieved, and gives motivations to study a novel proposal of dilaton
dependent uplifting mechanism for which no numerical studies has been performed
before. We find that in this case it is actually possible to get a dS vacuum,
but still leave open the question of a more precise discrimination feature the
good uplifting mechanisms should satisfy.
