I have the 6600 and at times I've had it suck fabric into the bobbin abyss. Then I started using a folded fabric starter piece and no more sucking. I adore the built in walking foot and I use it for piecing as well as quilting. I wouldn't give it up for the world now that I've had it. I'm not using the single hole plate because I'm moving my needle position for a scant 1/4" and using the walking 1/4" foot.
One thing I don't like about the 6600 is that it seems to be fussy about using different thread in the top and bottom. If I do this, it vomits. It vomits cheap thread too. It's like a temperamental Ferrari.