I just replaced a WD Black 640 3 years into its life. Blacks have a 5 year so they RMA'd it and sent me a 750 in its place.
I do however have a Seagate drive laying around somewhere that has almost 10 years on it and it still functions flawlessly. But it is admittedly smaller given its age and that may contribute to lifespan. Either that or Seagate has slipped in the last decade.