  I review the observational prospects to constrain the equation of state
parameter of dark energy and I discuss the potential of future imaging and
redshift surveys.
  Bayesian model selection is used to address the question of the level of
accuracy on the equation of state parameter that is required before
explanations alternative to a cosmological constant become very implausible. I
discuss results in the prediction space of dark energy models. If no
significant departure from w=-1 is detected, a precision on w of order 1% will
translate into strong evidence against fluid-like dark energy, while decisive
evidence will require a precision of order 10^-3.
