I just bought a new charger, to replace a new charger that I bought to replace the original charger that came with my 2008 MBP.
Probably apple would have replaced my the original charger when it broke in 2009, but I was no where near an Apple shop and I needed it urgently. Then again, maybe they wouldn't have, because I'm not sure the fraying problem was that commonly known.
The second time they would not, because the 'genius' argued that it was not 'frayed enough' and another problem was causing the drop outs in power. This really got my goat - i.e "its broken, but not broken in the specific way that we can replace it."
At this rate I'm buying a new charger nearly once a year and thats f$$cked.