I've had my 6600 for almost 5 years...and it is a "high-mileage" machine! I have never had any trouble at all with it, and love it. The built-in walking foot is great, and would be reason enough for me to upgrade from 6500 to 6600. I take it in every 12-18 months for servicing/cleaning. My repairman has been servicing sewing machines for almost 30 years, and he told me the 6600 is the most-liked machine by his clients, and it needs fewer repairs than any other machine.