I have tested out three different cams I got off eBay over the past few months and all of them seem to share the same problems. Two of them were CCD with infrared and were a little too large for my tastes, and one of them was a very small CMOS camera without infrared.
Anyway, on all of the cameras I used, during night driving the headlights of other cars coming towards your car really blind out the display, which is pretty disappointing. I tried mounting the cameras down by my license plate as well as way above it, but it didn't seem to matter. I think the lenses are desperate for light when it's dark out, so they "grab onto" as much as they can get in these conditions. Not good when you have headlights coming towards you. The CMOS camera was affected a lot more than the CCDs, but even on the expensive 1/3 CCD I bought, it was still pretty bad.
A similar problem also occured when it was clear out and the sun was setting. If you're driving with the back of your car pointed at the sun and it's really clear out...the direct sunlight also causes display issues. On the CMOS cam, the image would even turn brown/red.
I also noticed that the wider viewing range of the lens, the further away the images on the screen appeared to be.
With the 130 degree cam I had, a car that was almost touching my bumper when I looked at it through my rear view mirror, appeared on the camera like it was at least 1 car length away from me. That could cause problems..
The plus side to the 120 - 130 degree camera was that the viewing angle was so wide that a car coming up to the left of me that was only visible at that point through my left mirror was STILL visible on the camera for as long as it was visible in my left mirror.
The little 70 - 90 degree camera on the other hand gave a more accurate view of the distance between other cars and me, however, I basically could only see what was directly behind me and not what was coming up on my sides like I could with the wider angle cams.
The other one was somewhere between 90 and 120 but still wasn't quite right in either department.
So there doesn't seem to be a good compromise here. Seems like it's either wider view with incorrect distance, or narrower view with nearly correct distance.
I may be able to live with that, but there needs to be a way to get around this problem with incoming car headlights blinding out the display at night.
As long as these problems persist, I can't really see how these rear cams could realistically be used as "secondary rear view mirrors" like everyone hopes. Right now I think they're really only useful for what they're meant to do...helping you reverse.