I happened to be in BB the other day when I looked over the shoulder of a customer getting a demonstration of the 60Hz vs. 120Hz difference. They had a 1080p source into a 1080p capable TV, 32" LCD IIRC. (I don't know what the source was, "TV" or 24fps movie.) The demo was a split screen that said "120Hz On" on one side and "120Hz Off" on the other. It was presenting several slowly moving objects as they changed from one side to the other. None was rapid, and some text was included. In every case the "Off" side showed a softer or blurrier (is that a word?) image of the moving parts vs. the "On" side that was crisp and detailed. The still parts of the image were equally crisp on both sides - only the moving parts showed the blurriness. Has anyone else seen this demo at BB ??
The difference was impressive, but I think it might have been staged quite a bit! There was no evidence that I could see of "judder" (which in my understanding is the real consequence of the 3:2 pull-down of 24fps movie content with 60Hz refresh) unless that very bluriness is judder. However, I have a 52" p-capable TV (i.e., no conversion needed for a p source) with only 60Hz refresh and I have never seen an HD image that looked that "soft", when moving vs. crisp when still, even at the larger size. I have to admit, I really don't know what judder is first hand as I don't think I have ever seen it unless I just did at BB and didn't know it. If it's something else, it doesn't cause a negative reaction in me. I guess I would need someone to point judder out to me. Maybe that's what the guy at BB was doing, but again, I think it was exaggerated.
The point is with p-capable equipment I think the real issue is with judder in the 60- or perhaps even 72-Hz refresh rates. Per the first article teamerickson linked, there is no difference in the content and as long as you're not doing any conversions then what you see resolution wise, i vs. p, is identical. My 1080i-only A2 looks great on that TV, and from what I have learned even if it output p there would be no discernible difference in resolution. It all comes down to whatever advantage 120-Hz refresh rate gives you...