I recently picked one of these up for all kinds of uses from flying, to holidays and car dash cam recording. Turns out it's potentially really good at doing it all. I only have a 16GB microsd at the moment, which records about an hour and a half of high quality footage, and the batteries last about as long, but the footage quality is great and the official iPhone app works really well too.
I upgraded the cameras firmware and that added a lot of new useful features. The WiFi connection is really impressive, but I wouldn't use it when flying in case of interference. But that's cool as it turns out it's easy to adapt the Yi into an 2.5K FPV camera too - something I'm going to do when I get the time.
I'm really impressed with the little thing, especially at the price of £40 odd.