If cared for properly, a quality down bag should last for decades. For most serious outdoorsmen, a quality down bag is one of the best investments in outdoor gear they can make.
I own a Marmot and a Feathered Friends and they are both great bags. I have walked and paddled over 15,000 miles with them. Western Mountaineering has a well-deserved reputation on par with the best manufacturers, and far better than low end bags. Good luck telling the typical WM owner there's a better option.
Store down bags uncompressed, dry them completely after every outing, clean them exactly as the manufacturer suggests [no more often than needed to maintain good loft] and a good down bag will serve you well.
