I just dug up this thread because it seems to be indirectly related to a problem I am having... I had purchased a Mitsubishi DP900U about 2 years ago, and it was a wonderful monitor that I could look at continuosly for long periods of time with little or no eye fatigue... The monitor developed a problem of some sort that would cause the screen to appear to flicker as if it had momentarily lost power, similar to what the screen does when you 'degaus' it. It would do it sometimes 4-5 times in a row in rapid succession. It became quite irratating and wanted to replace the monitor before it might die on me, and while it was still under warranty.
I contacted NEC-Mitsubishi about the problem and they sent me a new monitor. This was a refurbished DP900U, but it was horribly unsharp. It was causing me to have headaches and eyestrain within a few minutes of using it. I called them back and told them of the problem. They sent me yet another refurbished DP900U. I continued to use the original monitor with out any problems for another week, and finally got around to setting up the 2nd refurb'ed monitor. On initial inspection, everything looked good with the second monitor, and boxed up my original monitor and sent it back. But after using this monitor for a couple of days, I realized that I was again experiencing the headaches and eyestrain again, albeit after using the monitor for a longer length of time.
I called NEC-Mitsubishi again today and they agreed to send me a new DP920 instead. I don't know if there is a real point to this, but I have come to the conclusion that there is probably a real difference between individual monitors, even within the same model numbers and specs. I wish there was some measure of sharpness or test that could kind of standardize or quantify differences between monitors and aid in setting them up correctly.
If you have a good monitor and everything (Refresh rates, resoloution, etc) is setup correctly, and you are still having bouts of eyestrain, I would be taking a hard look at the monitor and see how sharp the text really is. It may not be as sharp as it should be....
Dave