In this paper we give non-trivial applications of the thermodynamic formalism
to the theory of distribution functions of Gibbs measures (devil's staircases)
supported on limit sets of finitely generated conformal iterated function
systems in R. For a large class of these Gibbs states we determine the
Hausdorff dimension of the set of points at which the distribution function of
these measures is not α-H\"older-differentiable. The obtained results
give significant extensions of recent work by Darst, Dekking, Falconer, Li,
Morris, and Xiao. In particular, our results clearly show that the results of
these authors have their natural home within thermodynamic formalism.Comment: 13 pages, 2 figure