I can speak to the power of shadowing for improving spoken language ability. If you check out techniques discussed on the How To Learn Any Language forum [1] where many of the foremost polyglots and hyperpolyglots hangout, you'll see that Shadowing and L-R are basically accepted as fundamental techniques.
It takes real determination to correctly shadow though, like patio11 said you need to reproduce the sample _exactly_. This can cause you to spend an hour trying to perfect <5min of speech. But it's extremely rewarding.
For example, when I was learning Mandarin I chose a 20 episode (1hr each) tv show as my shadowing material. It took close to half a year of working on it almost every night to finish. But afterwards I had "somehow" developed a deep sense of what words/phrases/idioms/etc _felt right_ to say when speaking and how to say them in that oh-so-close-to-native like way. The topic has been extensively discussed on the learn any language forums. But suffice to say, if you want to improve your spoken ability, doing a lot of shadowing would help.
It takes real determination to correctly shadow though, like patio11 said you need to reproduce the sample _exactly_. This can cause you to spend an hour trying to perfect <5min of speech. But it's extremely rewarding. For example, when I was learning Mandarin I chose a 20 episode (1hr each) tv show as my shadowing material. It took close to half a year of working on it almost every night to finish. But afterwards I had "somehow" developed a deep sense of what words/phrases/idioms/etc _felt right_ to say when speaking and how to say them in that oh-so-close-to-native like way. The topic has been extensively discussed on the learn any language forums. But suffice to say, if you want to improve your spoken ability, doing a lot of shadowing would help.
[1] http://how-to-learn-any-language.com/forum