I once witnessed a cart go flying all the way across the lot only to hit a car that someone obviously parked way off in the corner to avoid getting dinged. It's like that cart had radar! If I could have, I would have stopped it.
I've seen that, too. Not funny for the person whose car is hit, but ironic in that the place can be practically empty, and the cart seems to find that one lone car.
I almost always return my cart. Most of the time, I park right next to the cart corral, so it's very easy. I got into that habit when my kids were little and I didn't want to lock them in the car on a hot day, or keep them outside in the cart on a cold day. Where I shop, the corrals are usually pretty far down the rows, so it's very easy to find a spot next to one unless it's an especially busy day at the store, and the extra 10-15 yard walk is worth it for the convenience.
If there is no corral anywhere near me and the weather is so bad, or my child is sick, or there is some other compelling reason not to search out a corral, I will leave the cart as securely as I can, either with two wheels up on the grass, or at the lowest point I can on the X.
Seems that most of the time if I see someone leave a cart, they have similar reasons, but occasionally I see those lazy farts, no kids, weather is great, corral is 10 feet away, yet they just don't seem to care, and just leave it whereever. They are the annoying ones.