I have figured out 'whodunit' in pretty much every case, but when it comes to 'howdunit' I would say I've figured out about 40-50, mostly from the very beginning of the series when the plots weren't as sophisticated and also from more recent episodes as quality has declined.
Detective Movies Contest 2013: Information Thread Current Faceoff
"The energies of our system will decay; the glory of the sun will be dimmed, and the earth, tideless and inert, will no longer tolerate the race which has for a moment disturbed its solitude. Man will go down into the pit, and all his thoughts will perish. The uneasy consciousness, which in this obscure corner has for a brief space broken the contented silence of the universe, will be at rest. Matter will know itself no longer. 'Imperishable monuments' and 'immortal deeds,' death itself, and love stronger than death, will be as though they had never been."