To resolve at least three issues with the adapter Apple is going to launch a redesigned MagSafe power adapter:
Of the potentially more serious problems are reports dating back to last year that the thinner of the two adapter cords has a tendency to heat up and fray near both the power brick and the MagSafe connector, creating a potentially serious hazard. As noted in a AppleInsider report from March, Apple has made at least one attempt to remedy this problem by increasing the strength of the plastic insulator where the cord meets the MagSafe connector.Source: Apple Insider
Another, more recent issue is a tendency for the tiny pins inside the MagSafe connector to improperly spring back into place, resulting in a faulty connection between the MagSafe connector and the MacBook Pro's built-in power adapter port.
And lastly, some adapters -- including those owned by AppleInsider -- are showing signs of a somewhat benign defect where the LED indicator light on the MagSafe connecter will intermittently shut off even though the adapter continues to charge the MacBook Pro.