I absolutely love mine! I've had it for just about two years and I'm convinced I can sew anything with it. FMQ is great right out of the box, with auto tension and plenty of space. This replaced a 7700, which had replaced a 6600. No regrets at moving up to the 8900.
One of the things I love is the large foot pedal. It's about twice the size of my old one.
I honestly can't think of anything I don't like about it, and I have a Juki as well (the 600) but prefer the 8900. One thing you should do is ask the dealer to throw in the Accufeed 1/4" foot and Accufeed Open Toe foot. They are all I use, except for the free motion foot, which comes with the machine.
If price is an issue, you could look at the 8200, which is the same except for the number of stitches (but still plenty) and the accessories that come with it.
Any specific questions?
Lynda