What's the size of the visible area in Mobile Safari on the iPhone 5 in default configuration, in landscape and in portrait orientation?
According to Kyle Larson's article iPhone 5 Web Design, the resolutions are:
Portrait: 640 × 888 px (= 320 × 444 double px)
Landscape: 1136 × 392 px (= 568 × 196 double px)
That is with navigation bar, i.e in default configuration, like I wrote in my question.
According to @astletron, the resolutions are:
Portrait: 640 × 920 px
Landscape: 1136 × 424 px