dkimleeNot dramatically longer, but longer. Very good for drinks, like Irish Coffee, but I wouldn't recommend them as replacements for your everyday coffee cup.
dkimleeThe problem is that so much heat is lost through the surface, after all, heat rises. They are going to work better for cold drinks, frankly, but, at least you don't burn your hands. Reviews make me think they might be reasonably sturdy, most double wall stuff breaks very easily, with the only exception I've found to be the Sun's Tea line, which are as tough as any other glass (but, only straight wall, so, not so pretty).
ChaostrophyThat really depends on how you prep the cup for coffee. For coffee shops, and pro home brewers, it is necessary to preheat your vessel with boiling water. That way it keeps your cup from sucking all the heat from your drink. These cups are designed well for both hot and cold drinks, but from their titling and design I'd assume they're for hot drinks.
imnotdanWhile I do exactly what you talk about I suspect it doesn't matter, as the mass and specific heat the glass is trivial compared to the water. I should measure things and find out, but I suspect putting a sheet of plastic over the top will have more effect.