My point wasn't that anyone should necessarily buy Monster Cable. I don't have a single monster cable in any of my three audio and A/V systems (and there was a time when I first got into this hobby many years ago when I did). I agree with folks who have said that there are cheaper alternatives that are as good or better.
In my friend's case, he was having a bunch of people over to watch a sporting event in high def, and he was unhappy with the video quality, and Radio Shack was right up the street. My point was simply that he upgraded from the super el-cheapo garbage HDMI cord that came with his component and it solved his problem.
So, in term's of the thread's key question -- does an upgraded HDMI cable make a difference, the answer is that it sure can, at least in the case of my friend, and he and I were both able to discern a clear difference (as was his non-audio/video/file wife). Whether te upgrade needs to be "high priced" or not would require somebody to do an HDMI cable shoot out and figure out what offers the best bang for the buck.