I have a 2008 model aluminium macbook. November last year I managed to break my charger by running over it with my desk chair. i went to the mac store, bought a new "l-shaped" charger and it was all good. In January it died. It spluttered for a few days before it stopped charging my mac all together. Took it to the mac store, they replaced it. A month later, same thing happened. Replaced it, no questions asked. It's been two months and last night it died again. I've got an appointment with genius bar on saturday but I'm guessing they'll just do the same thing and replace it again. What is my macbook doing to these chargers? I'm using my sisters charger now, no problem...
My MBP kept doing that, too. Ultimately, they replaced the power inverter board, (I think that's what it's called) but I found that my adapter would work better in Pittsburgh, so it might be a powerline issue. Think sine waves being weird from E&M Physics.
My suggestion would be bring your MB in so they can test it as well.... Sounds like a bad power inverter.