I use my 6600 on a nearly daily basis for much of the year - zero troubles. Not even after I turned my (then) 8 year old niece loose with the machine for several days in a row. I had to fish broken needle bits out of the bobbin area, but even with all of her well-intentioned abuse the machine was just fine. LOVE that thing!
The very first sewing machine I bought for myself in the 90's was a very inexpensive Kenmore made by Janome. I abused that poor machine for many years, never took care of it properly, never cleaned or oiled it (all out of ignorance), sewed things with it it was never designed to sew through, broke countless needles doing stupid stuff like yanking the fabric...and that "cheap" machine STILL works just fine!
As far as I can tell, Janomes are bulletproof!
There's always a chance you'll get a dud, but I'm a big fan of the Janome brand and I feel very confident in their quality. If my 6600 ever perishes I'll be buying another one the next morning!