The audio on many HDV cams like the popular Sony FX-1 is noticeably inferior to some relatively modern DV cams like the Sony VX-2100, partly due to the design and partly because the audio compression of HDV is inferior to DV.
I always at least use a directional Sennhesier external mic mounted on the camera to shoot gonzo style, and that improves the audio a lot. Because most external mics are mono however one has to remember to fill in the second channel of audio when you edit the footage however to make it sound like stereo. If I were filming a dialog heavy feature movie I would mount a mic on a boom pole and have someone who knows what they are doing handle the boom.
