Of course no one has had an issue with it, or they wouldn't be here. It's an odorless gas and gives off no warning. By the time you'd know you had a "problem" you'd be dead. Co scares the hell out of me! A guy I know had his own son die of it while sleeping in the cabin of a boat. Kid went into the berth to take a nap and never woke up. Call me crazy but I always have a Co alarm in my tent when I run the stove, and I have two in my trailer for the heater. Not taking any chances. I've never had an alarm go off but I sure have more peace of mind.
Co displaces oxygen and is heavier and basically fills from the bottom up. I've never had a problem but have heard of people leaving the propane stove on all night and poisoning themselves. I don't worry about it enough to carry a detector but I also realize in some conditions it could be a problem
Wood stoves shouldn't be an issue except for burning down the tent. I'm sure its happened before. If using propane make sure its a catalytic type like the Buddy heaters if you plan on leaving it on all night. Most of those type have a CO sensor in them and should shut off if detected. We usually leave a window partially open either way for some air flow.