I discovered this method by accident and then read about it here later. The best ribs I've ever Q'd to date came when I went to look to see if the ribs were done (having left them on longer than I initially intended to). I picked up a rack using my hands in the middle of the rack and they bent and mildly started to split, at the bend where I was holding them. It was obvious they were totally done so I took them off. They ended up being my best ribs yet.
So, that is the method I use now. Pickup the rib rack in the middle, let them bend naturally or give them a little help to bend with your other hand. If the meat starts to split like you could easily break the rack in half the ribs are done to perfection. Note: my personal preference is for ribs on the more well-done side, I don't like ribs that are chewy or still have un-rendered fat in them.
At least, this is my interpretation of the bend test.