One of the most common things we see in our shop is MagSafe power adapters with damaged wire insulation and/or fraying where the thin cord meets the power brick or where the cord meets the actual MagSafe tip. While many consider this the result of a design flaw (coupled with the fact that Apple does offer free replacement in some situations), the simple fact is that these conditions are completely avoidable.
It is my opinion that Apple’s offer to replace these damaged cords is more a customer service measure than a reaction to any design or build quality issue. I have three 85 watt adapters from the original MacBook Pro; they are the larger variety, about four years old, and in fine condition. The logical solution is to not let there be tension at the two crucial points of the cord.
Most commonly, fraying at the power brick end is the result of wrapping the thin cord too tightly when the adapter isn’t in use. Wrap it more loosely, and wrap it such that the cord remains perpendicular to the power brick. This eliminates the strain. The same principle applies for the MagSafe tip end: keep it perpendicular to the computer to eliminate strain, but also never pull on the cord to remove the plug from the power port.
Replacement adapters are $79.99.