This may be old news, but I thought it was a worthy suggestion to prolong the life of any Mac power adapter cord that has the small u-shaped sliding cord keeper. The idea is useful enough that it might save Apple some complaints about their shorted-lived cords.
Slide the cord keeper right up to the reinforcement at the male end, as seen in the image at right. Insert the plug into your Mac. About three inches from Mac, make a loop and double the cord back on itself and insert the doubled portion into the cord keeper to maintain the loop. This reinforces the connection to the computer, holding it at a 90 degree angle from computer. It also serves as a shock absorber, as the loop will release first before pulling the cord from the computer.
[robg adds: I have a setup at home that's conducive to fraying the power cord -- the power cord runs out the side of the MacBook Pro, then backwards through a hole in the desk, leading to some direct pressure on the connector. I hadn't thought to use the cord keeper, but this is a great solution -- I put the clip somewhat further away from the power connector, and made the loop larger, than seen in the provided photo above. I feel much more comfortable with this setup; there's now no direct backwards pressure on the cable.]

