With data now at hand, not only there are several interesting, plausible theoretical models within the standard astrophysical agenda to explain all the CRs detected so far, but there could indeed be too many. Perhaps yet unexpected degeneracy problems will appear, even with the forthcoming data of the Pierre Auger Observatory, a topic which till now has not been a subject of debate. In our view, Occam's razor imposes that all standard astrophysical models be eliminated before embarking in the consequences of explanations involving physics beyond the standard scenarios. However, should this be the case, the prospect for encountering a profound scientific revolution are endless. The puzzle of UHECRs may have something to say about issues as fundamental as local Lorentz invariance: On the one hand, the absence of photo-pion production above the GZK-limit would imply no cosmogenic neutrino flux and possibly undeflected pointing of the primary back to its source. On the other hand, a significant correlation of TeV-antineutrinos with directional signals at EeV energies will validate Special Relativity to an unprecedented boost factor of 109, several orders of magnitude beyond current limits. Additionally, contrasting the observed quasi-horizontal neutrino flux with the expected neutrino flux can help constrain TeV-scale gravity interactions and improve current bounds on the fundamental Planck scale. An optimist might even imagine the discovery of microscopic BHs, the telltale signature of the Universe's unseen dimensions. At the time of writing, new data is being collected at Pampa Amarilla. Whatever happens, in T-2 years we shall witness the lift off of a new era of cosmic ray physics.
During the last few years, we have benefitted from discussions with several colleagues and collaborators, among them, Felix Aharonian, John Bahcall, Paula Benaglia, Peter Biermann, Elihu Boldt, Murat Boratav, Yousaf Butt, Analía Cillis, Jorge Combi, Jim Cronin, Tom Dame, Chuck Dermer, Seth Digel, Eva Domingo, María Teresa Dova, Luis Epele, Jonathan Feng, Francesc Ferrer, Haim Goldberg, Francis Halzen, Tim Hamilton, Carlos Hojvat, Dan Hooper, Michael Kachelriess, Mike Loewenstein, Tom Mc Cauley, Gustavo Medina Tanco, Pran Nath, Carlos Nuñez, Tom Paul, Santiago Perez Bergliaffa, Brian Punsly, Olaf Reimer, Steve Reucroft, Andreas Ringwald, Gustavo Romero, Esteban Roulet, Subir Sarkar, Sergio Sciutto, Al Shapere, Paul Sommers, Guenter Sigl, Todor Stanev, John Swain, Tomasz Taylor, Dave Thompson, Peter Tinyakov, Alan Watson, Tom Weiler, and Allan Widom. We would like to thank several of the collegues mentioned above as well as Ray Protheroe for allowing us to use some figures from their papers in this review. We thank Julianna Gianni for inspiration. The work of DFT was performed under the auspices of the U.S. Department of Energy (NNSA) by University of California's LLNL under contract No. W-7405-Eng-48. The work of LAA has been partially supported by the US National Science Foundation (NSF) under grant No. PHY-0140407.