Most of the arguements are based on the traditional SD TV displays and computer monitors. They are particularily based on a raster scan type display. Most fixed pixel displays will eliminate a great deal of the issues of interlaced vs progressive. Since fixed pixel displays are progressive by their nature, the picture is built in a pixel array memory that is then transfered to the display in a progressive manner. Once a pixel is "on" it will remain on until it is turned "off" on a sucessive update. There is not any decaying of phosphers to contend with, so the issue about only half the pixels being shown at any given time will drop out of the issue as they are all being displayed. On CRT type displays the phospher persistance and excitation cutoff is such that all of the pixels will be lit for the most part, although there is some difference between scans.
Motion blurring is one thing, but at 1920 x 1080 it becomes very difficult to distinguish from the bluring effect due to pixel straddling. Excerpt from
http://members.aol.com/ajaynejr/vidres.htm
Quote:
Pixel Straddling
(Affects resolution of the recording of live subjects, also the net resolution after scaling of the picture to different pixel dimension.)
Some cartoons are generated directly on computer screens. For them, picture details may be consistently lined up with the pixels, and for a 720 x 480 pixel DVD frame, the resolution can be consistently 720 x 480.
For the televising or recording of live subjects, the scan lines and (for digital video) the pixels horizontally will not consistently match up with fine details in the subject material. This can be seen if the camera is panned across details that are as fine as the pixels, those details will change from sharp to blurred to sharp again. For this reason, there are some people who will say that a 720 x 480 video frame has far less than 480 lines of resolution vertically or 720 pixels across horizontally.
As we mentioned earlier, a pixel or a small stretch of a scan line must be all one color. Going back to an earlier example of looking at a scene through a silk screen and painting it on canvas one dot at a time, if there is both black and white showing through the same hole in the screen, you have to choose the in between color of gray.
In the diagrams below we show some examples of pixel straddling in the horizontal direction. A moire pattern is the result of picture details going in and out of straddling (in and out of phase with the pixels) over a large area.
Of course we can use twice as many pixels or scan lines to eliminate the straddling but sooner or later the bandwidth needed for the video signal is too large to fit in the allotted broadcast channel or the amount of data is too large to fit on the DVD.
Pixel Straddling Examples (greatly enlarged)
 Original source is on top, video representation is on bottom. The red and white dashes along the top denote the pixel positions.
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Bluring from pixel straddling can be as much or more than the bluring due to interlacing and with the naked eye you don't necessarily know the difference. In fact should the object line up on one pass to the next, the motion blurr can actually be decreased because of one pass being sharp, whereas with progressive scan there is only one pass, so it will just be blurred.
Also the effects of resolution is not given the full weight when this subject is discussed. Take a 40" wide (not diag.) HDTV screen for example. It will be made up of 1920 pixels wide or 1280 pixels wide. This would translate to a pixel width of .021" and .031" respectively. Right there you have a 33% better chance of not getting pixel straddling with the 1920 pixels. The vertical chance difference is also 33%, so the motion blurr is not the only thing to consider. In fact since the motion is normally not covering the entire screen, the pixel straddling blur could effect the overall picture more than the motion blur. Sports would be the opposite as the background tends to be the motion more so than the subject as the camera follows the subject.
Also with 1920x1080 having 33% more total pixels than 1280x720, the motion blurring is less noticeable than the difference would be if they were both being at the same resolution.
The biggest problem with 1080i is bandwidth, or the lack thereof. Most motion distortions are not blurring, but rather pixellation due to insufficient bandwidth. This is the station's choice and if you live in an area where they are compressing your 1080i signal to the point that fast moving objects end up a bunch of small boxes, it is the station, not the technology. Small boxes is pixelation not blur.
In side by side blind (excuse the pun) tests there have been studies that most people could not tell any difference in the two formats.