I've used the same MagSafe that came with my MacBook Pro throughout its life.
The Adapter is almost 3 years old and it still works fine and I use this machine every single day. I disconnect and reconnect the cable at-least once or twice per day and I'm constantly moving the laptops orientation (Putting stress on the cable as I do so). The only issue I've encountered is the little LED inside the end of the connector doesn't work anymore. BUT the connector still charges fine.
In comparison with the old power connector they used (The Circular non-MagSafe one) I had to replace two of those adapters within 14 months of ownership of my PowerBook G4. Those adapters were crap and both times that it died I had exposed electrical wires at the connector end that plugs in to the Laptop. I didn't abuse these adapters, just normal wear and tear from plugging in and out.