Yes, there have been papal resignations before, and the possibility of one has been anticipated in recent years. But the last time a pope actually did it was 77 years before Columbus fetched up in the New World, and that was to permit the resolution of a schism in which three men claimed the See of Peter.
That the Roman Catholic Church is in as serious a crisis now as it was in 1415 is a nice question. The last third of the 20th century saw a remarkable enhancement in the prestige of the papacy, thanks to the charismatic leadership of John XXIII and John Paul II, respectively bringing the church into the modern world and presiding over the collapse of the Soviet empire.
But the last decade has seen that prestige squandered by the rolling abuse scandal. Following the Church's lurches from crisis to crisis, its over-the-top denunciations of civil authorities and contemporary mores, it is hard to resist the conclusion that here is an institution suffering from post-traumatic stress.
Curiously, this is the third time in history that a Benedict has resigned the papacy. The last time it was Benedict IX, a dissolute scion of the Roman nobility whose departure from office in 1049 led the way to the great reforming papacy of the later 11th century. Among its principal reforms was bringing the hammer down on bishops who had bought their offices (simony) and kept wives (Nicolaitism).
If the resignation of Benedict leads a new pope to bring the hammer down on the bishops who have covered up clerical sexual abuse, he will be counted a worthy successor of Leo IX, Alexander II, Gregory VII, et al.