I forgot to renew my registration one time and I woke up to find my car gone (I had been living at an apartment complex at the time). It was towed away in the middle of the night. I was convinced it was stolen. Came to find it was because my registration was expired. I was more pissed about the apartment complex allowing towing companies to take your car in the middle of the night.

So yeah, always remember to pay your registration fees.