  In this paper, we derive simple and general perturbative formulas for the
flavor flux ratios $R_{\alpha\beta}=\phi_{\nu_\alpha}/\phi_{\nu_\beta}$ that
could be measured at neutrino telescopes. We discuss in detail the role of the
uncertainties of the neutrino mixing parameters showing that they have to be
seriously taken into account in any realistic discussion about flavor
measurements at neutrino telescopes. In addition, we analyze the impact of such
uncertainties in telling the standard neutrino oscillation framework from
scenarios involving, e.g., neutrino decay and we find that the ratio $R_{e\mu}$
is the most sensitive one to "new physics" effects beyond the Standard Model.
We also compute the more realistic muon-to-shower ratio for a particular
configuration of the IceCube experiment, observing that using this experimental
quantity a clear separation between standard and non-standard neutrino physics
cannot be obtained.
