I've never heard anyone else having problems with RX300 locking up. It must be corrupt firmware installation. Have you tried flushing 2.3G again? Make sure your camera's battery is fully charged (just to play on a safe side). I had firmware v2.2G installed, downgraded from v2.3G just to test it. Both firmwares worked perfectly fine for me, and since the day one I purchased this camera, it never ever gave me a single problem, except compass screensaver sometimes sits on North (but correct compass information is still being saved properly, we tested it in Driving Recorder). I am not even using screensaver anymore, so that thing is less than minor problem for me.
GT680W is a great little camera too, but the fact that doesn't have battery powerful enough to keep your dash cam on and recording when unplugged from lighter plug in your car, threw me away from it. Say one example... God forbid you're in a bad accident where your car battery completely got disconnected, or any other reason for losing power in your car. You dash cam stops recording instantly... but even bigger problem is, if it stops recording so abruptly, it could easily result in corrupt video file without any possibility for recovery. Not very good in case your evidence simply disappears. RX300 keeps recording and that's what I love the most when it comes to RX300.