OK, just tested it out in a number of scenarios while running a few errands around the city -- it's really hit or miss. When pulling up to or backing up to our garage door, it's VERY accurate. It said that I was 20 inches away, and sure enough, it was pretty damn accurate.
However, when pulling up to a parking spot at Walgreens, where the concrete barriers are set down so that your car doesn't go past a certain point, it kept telling me to STOP and beeped even though I could visually judge that I had plenty of space left. The on-screen display showed a red horizontal line going through the bumper, signifying that I had gone PAST the barrier. I got out of the car, and the front bumper was about 12 inches away from the barrier -- in other words, I had plenty of room.
For the last test, I pulled up to my local donut shop into a space. There's just a curb that runs in front of all of the parking spaces in the strip mall. As I pulled up, it again beeped at me and told me STOP. It again put a red line through the bumper (like at Walgreens) to, I guess, tell me that I can't park. But again, got out of the car, and I had a good foot or so left to go.
So it seems as though it's good if it's a vertical wall in front of you. Not so accurate if it's a low-lying object, but still better than nothing. And that would make sense because how the hell is the camera going to be able to accurately predict how far away it is when it's out of sight? It can see a wall pretty clear as day, but the barrier/curb would only initially be visible to the camera, then disappear from view as you get closer (obscured by the hood). So it's doing some kind of calculations based on the last known position and your speed as you approach (or at least, that's my guess). I'm sure it'll get better with time.
