I do love my Horizon. I jumped from the 6500 to the Horizon -- got one of the first. I liked the accufeed that the 6600 had but I wanted a free arm so I waited. The harp is nice and large (11"x4.5"), I have used the free arm a lot, the stitches are more adjustable, there are more stitches and it has a lot of extra lighting. I also like the fact that I can open the side door and easily clean out the top of the machine when I sew on really linty fabric (think vinyl and fleece) It is wonderfully quiet. The one drawback (for me) is that when they made the 7700 they did not include the separate bobbin winder that was on the 6500 (and I believe 6600). I use the accufeed for most of my piecing/sewing so I have not had the problems going over lots of layers that others had early on -- I have made a ton of pillow cases and go over 12 layers or so when I am doing the sides and it goes over just fine.
As Iowastitcher indicated, the Yahoo group is a great place to ask questions.