Dan Banks answered
Health?
The official Vatican line is that Pope Benedict XVI resigned due to his deteriorating health. He had been advised by his doctor not to make long-distance flights and thus he believed that he could no longer effectively carry out his duties as the head of the Catholic Church. Having said that, traditionally Popes carry out their role until they drop dead.
Politics?
It has been suggested that the Pope had political reasons for resigning as this point in time. By doing this, Pope Benedict XVI could influence the election of his successor, and thus keep his conservative ideology alive for at least another Papal term.
Regardless of the motive, it is very strange that Pope Benedict XVI has taken this decision, especially because he is the first pope to resign in nearly 600 years!
Conspiracy?
However, I am not one to shy away from a good conspiracy theory. Some people have rather amusingly suggested that it was strange that the pope resigned on that exact same day that the full extent of the horse meat scandal broke in Europe. Is Pope Benedict XVI the head of some sort of international-meat-trading-consortium which specialised in selling horse meat for knock-off prices, and disguising it as beef? Unlikely, but food for thought nonetheless.
However, I am not one to shy away from a good conspiracy theory. Some people have rather amusingly suggested that it was strange that the pope resigned on that exact same day that the full extent of the horse meat scandal broke in Europe. Is Pope Benedict XVI the head of some sort of international-meat-trading-consortium which specialised in selling horse meat for knock-off prices, and disguising it as beef? Unlikely, but food for thought nonetheless.