Shimano 105 vs Ultegra?

I know Ultegra costs more, but what am I getting for the extra cost? I've heard 105 shifts about as well (don't know if that is true); I've heard 105 has as long a live expectancy, if not longer (don't know if that is true either). If I don't have ambitions to ride in a future Tour de France, how do they compare?