Had mine not quite a year now. Got an "experience" one when folks traded them in for the 7700.
6600 is a really nice machine. Do I wish I had a larger harp area like the 7700? Of course I do! But since I already had one newish machine (3 yr old Husky) I couldn't justify the $$ until I saw the used machines they had.
It took some getting used to. I used to have problems with various thread - it didn't like some, and at first it didn't like different thread in the top and bottom. I don't have these problems anymore. Adjusted tension, and I guess the machine and I have become friends.
I love the Accufeed - biggest reason I got the machine. I was doing a ton of 1" strip piecing and boy oh boy did that accufeed help me zip through those. I bought it specifically as a FMQ machine, but I love piecing long strips on it.
I like the extra height lift on the presser foot - raises really high to get a quilt under the foot (my Husky doesn't do this).
Love the one button quick change needle up/down position. The best for FMQ.
I don't use the needle threader, but I do use the cutter. So far it's great. Wondering if it will ever need to be sharpened??