I don't have much of an opinion to express, but it seemed appropriate to write a blog entry anyway.
In his announcement, he cited poor health as the reason for his resignation; and though the conspiracy theorists will be having a field day, I see no reason to doubt the official line without evidence to the contrary.
This was one of those "do you remember where you were when you heard the news?" moments. I heard it at 11am at work; I was walking through the reception area, past the television that's almost permanently tuned to the BBC news channel. Not an item of news I expected to hear today, or any day. Never thought something like this would knock the dobbinburgers off the top of the news.