A friend got slapped with a fine over this. He's a foreign resident, and he changed hotels while on a trip. That information is bundled up and sent to the authorities, and they cross-checked him with the address he put on his travel form. Thousand baht fine.

FWIW, I brought this same friend to the police station where I'm a registered resident in Shanghai, so he could stay with me on a 72-hour visa. At the airport, he was told that if he doesn't register and it's discovered, it could affect his ability to get a visa in the future. This was only a few months ago.