I must say, and I've learned English a lot, and I mean a lot, from watching Seinfeld, over and over again, plus movies and other TV shows. I think this is extremely effective when you watch something over and over again. I personally watched Seinfeld between 50 to 100 times (not one episode but the entire series .. I know.. crazy..), and not necessarily because I wanted to learn English from it, but mostly because I've enjoyed it, well, a bit too much.