We investigate the relation between the distributions appearing in the study of ergodic averages of parabolic flows (e.g. in the work of Flaminio-Forni) and the ones appearing in the study of the statistical properties of hyperbolic dynamical systems (i.e. the eigendistributions of the transfer operator). In order to avoid, as much as possible, technical issues that would cloud the basic idea, we limit ourselves to a simple flow on the torus. Our main result is that, roughly, the growth of ergodic averages (and the characterization of coboundary regularity) of a parabolic flows is controlled by the eigenvalues of a suitable transfer operator associated to the renormalizing dynamics. The conceptual connection that we illustrate is expected to hold in considerable generality.2000 Mathematics Subject Classification. 37A25, 37A30, 37C10, 37C40, 37D40. Key words and phrases. Horocycle flows, quantitative equidistribution, quantitative mixing, spectral theory, transfer operator. L.C. gladly thanks Giovanni Forni for several discussions through the years. Such discussions began in the very far past effectively starting the present work and lasted all along, in particular the last version of Lemma 5.11 owns to Forni ideas. P.G. thanks L. Flaminio for explaining parts of his work and his hospitality at the university of Lille. Also we would like to thank Viviane Baladi, Alexander Bufetov, Oliver Butterley, Ciro Ciliberto, Livio Flaminio, François Ledrappier, Frédéric Naud, René Schoof and Corinna Ulcigrai for several remarks and suggestions that helped to considerably improve the presentation. We thank the anonymous referee for his hard work and thorough suggestions which forced us to substantially improve the paper. the IHES for the kind hospitality during the revision of the paper. 1 But see, e.g., [49,50,43,41] for earlier related results.2 Typical examples are circle rotations [52, 53], interval exchange maps via Teichmuller theory [55,28], horocycle flow [26,21].