Do you guys use these every time you drive, or accident protection? I mean I put my gopro's up for racing...and have seen the Russian videos of dash cams. I see the reasoning behind using one, but curious.
The idea behind the dash cam is for it to work at all times without you having to do anything. This is why Thenorm has configured it this way, so that it turns on and off with the engine. If you have to turn it on and off manually or plug it in each time, you'll do that for maybe a week and then quit because your drives will be uneventful, then it's pointless.
Any self-respecting dash cam begins recording automatically as soon as it receives power, so it makes sense to tie it to a fuse. If I'm not mistaken, the cigarette power outlet in the console is switched with the engine, so that's an option as well if your cable has the length.
The amount it records really depends on the size of the memory card you put in it. Most cams will continuously record in around 5-minute increments, providing you many different files. This splits it up so that if you do record something you want to keep, you only have to grab a small file instead of cutting down a multi-gigabyte file. Once the card fills up, it will begin overwriting the oldest, continuing on in a loop.
If you get a big enough card, you can typically hold hours worth of high-definition video. So, if you are in an accident, you have plenty of time to allow it to continue recording and still be able to go back and get the video you need. To go further with this, some dash cams give you the ability to hit a button on the camera, which will lock whatever 5-minute video file is currently recording. That file will then not be overwritten but allows you to continue recording on without fear of overwriting something important.
I'm getting the G1W-C dash cam, a very cheap but well regarded cam. I've read you can typically get about 6 hours of video with a 32GB card, which is enough to cover my whole week of driving back and forth to work before it starts overwriting.