I was shooting some slow pans yesterday on our JVC HM150 at 1080-25p and wasn't surprised that they exhibited the classic progressive jerkiness. I improved it a lot when I switched over to our best tripod (so I could actually pan slower). But would I get better results if I shot at 1080-50i and converted that to 25p on computer (they're ending up in a progressive project)? I'm feeling too lazy to do any tests today. I guess a slower frame rate would help too.
Of course zooming right out would also help. But I'm particularly interested in the shoot-interlaced-and-deinterlace vs shoot-progressive approach.
You certainly can shoot at 50i and deinterlace and down convert to 25p, and add simulated accurate motion blur to reduce judder. Shooting at 50i, the motion processing can be more accurate for adding blur than when adding it at 25p. This approach has the advantage of being able to convert to other frame-rates more accurately. If you can increase the shutter angle at the camera, it will similarly reduce motion judder, but it is harder to convert to other rates.