Here's a demo of before and after footage of night freeway driving comparing default auto exposure to the Tv mode exposure lock trick described on the HV20 enthusiast sites.
I used a Blackberry Curve with its photo viewer and a 75% grey 320x240 JPEG to lock the initial exposure, then adjusted the exposure up +10 for maximum aperture with zero gain using the "half-press" photo button technique to monitor the actual setting.
The auto-exposed version is unnaturally bright and extremely noisy, while the exposure locked and gain optimized version much better represents the actual perceived brightness, with nearly zero gain noise.
Best to view this video full screen non-scaled as the small image playback scaling hides a lot of the auto exposure noise.
I've had this camera for two days and am absolutely thrilled!