I have found that rib "done-ness" varies from region to region.
Most folks in the northeast feel that ribs should fall off the bone. I've always felt that was a sign of overcooked ribs. It's pretty subjective, depending on your audience.
I like to smoke at low temps, usually never above 220 for at least 2 hours. After that, the smoke no longer permeates the meat. I wrap in foil with just a touch of mop and leave the foil open on both ends. Another 2 hours or so at 220 or so and they should have a decent amount of give. The meat will tear clean from the bone, but not fall apart on you either.
It's all about experimentation and compromise between time and temperature. It's also relative to the fat content of the meat and thickness, etc.
Suddenly I'm drooling on my keyboard.