I have had a 6600 for 2 years - they are double those prices in France but I wanted one so badly. I wanted it particularly for quilting and I absolutely love it. Takes any thread without tension adjustment fiddling, quilts beautifully, I never have any wrinkles. I also have all the additional Accufeed feet and use them all. This year I got the Janome table specifically built for it and that made it even better.
You can get lots of info, technical stuff and comments on it on the Yahoo Janome 6600/6500 forum:
http://groups.yahoo.com/group/Janome6500