I'm glad I have mine. It gives me a little peace of mind, as I wouldn't want to be in a "he said she said" situation that was clearly the other person's fault.
They're not that expensive for a basic one, either. The G1W is the best affordable one. You can get them on Amazon for around $50, plus another $10 or so for a memory card.
I recently upgraded to a Rexing V1 and hardwired it to the driver's side fuse panel next to the door. It turns on when the car turns on and turns off when the car turns off. Here's my How-to thread for the install:
DIY: How to Hardwire a Dash Cam or Radar Detector
And reasons like this are why I have a dash cam (taken from my old G1W):