Well,

I'm bedoggled, I have this on my video http://droptodesign.com/test/Image0.jpg
in vegas. But it doesn't show up in my preview monitor. If you look at the corners, you'll see a slight drop off in light. I had a slight AE shift set, so I'm not sure if that was it or not. It's hardly noticable when the video is running. I've never run across this effect since I've had my Canon GL2, going on two years now.

I saw it specifically while capturing this tape, in the little Vegas capture screen, the 1incher.

I see it Steven.

Are you using a wide angle adaptor? Can I see slight deformation of the right hand edge of the door frame behind the happy couple?

Looks like some form of vignetting to me as well.
Either wideangle converter, or the camera is in it's wide mode anyway and also the aperture is wide open...
It's the lighter edges that show it up. Normally, with more detail in the image, it wouldn't seem so obvious.

Robin

Looks a lot like normal light fall-off at the corners of a wide open wide shot. This can run a stop or more. ALL lenses do this, but it is usually only noticeable in shots with large, flat areas.

This is just the Canon stock lense, which is what concerned me. I've never seen it before, and it's a lot less noticable in areas that have more light. Sooo, hmm, you recon it was some setting, since I wasn't using and adaptor?

the halo looks like its from oversharpening to me...

as for the vignetting, im unsure - probably from being wide open.

I'm going to do some testing under similar lighting, I'll see if I can recreate it.