I love keyboard navigation, +1 to infinity for this feature!
I have but one request: I usually open up questions in a new tab, from the newest or active questions pages, for example.
Normally, on Mac, I'd hold down the ⌘ (command) key while clicking on the link, or use the TAB key to shift focus to the link and use ⌘-ENTER to open the link in a new tab.
However, with the keyboard extensions, when a question has been selected (after pressing U, first question for example), there is no link focussed and the ⌘-ENTER will not open the question, at all.
Could this be implemented in the keyboard extensions? This probably has to be platform dependant, as the modifier key for Windows and Linux would be different.