In our anecdotal experience, Apple has been pretty good about replacing clearly faulty MagSafe power adapters—the ones that split or fray from faulty manufacture. But now they are making their replacement policy official and offering free MagSafe replacements for the MacBook (13-inch Late 2006), MacBook (13-inch), MacBook Pro (15-inch Glossy), MacBook Pro (17-inch). (We read that as all models that use the MagSafe power adapter). Bring in your bad MagSafes to any Apple retailer and they'll take care of you. [Apple via Cult of Mac]
Word to the wise on this: Apple is requiring all Apple Techs to call and verify on these. So that means if your local replacement source normally is able to replace things from stock (i.e. a local third party service house that is qualified by Apple), they have to have you wait in queue and chat the replacement over with AppleGSX as opposed to just doing an exchange over the counter. At least that's what we're having to do at the Service Department where I work (The Eugene Mac Store). Had a couple of pissed off customer's because of the new policy, so beware.