TL;DR--a student response to paper comments?

I've been thinking about the efforts of e-book purveyors to quantify our interest level in the books we read and had this idea for an invention:  what if someone could build a device or application that could track how students really respond to our comments on their papers?

There are lots of studies on this; that's how "minimal marking" and other trends in grading got started.  But what if we could know what they actually focus on, not through self-report or hand-coding responses based on video, but on real-time tracking depending on where their eyes went on the page?

Let me hasten to add that this ought to be done as an experiment with IRB approval and all that; I'd never advocate this kind of spying on people's reading routinely (although Amazon, B & N, and, as we all found out last week, Orbitz are all ready to do so).  But just think what we could find out:

• Do students, when confronted with a mysterious check mark, pause and wonder what the minimal marking means, or do they skip over it to go to the comment where something is actually written? If you return papers electronically and provide links in the margins, do they click on the links for an explanation? 
• If you've marked up a paragraph to show typical errors and then said something like "can you see other examples in the rest of the paper?" do they actually look at the other paragraphs to see if they made those errors? 
• Do they read the marginal comments or skip right to the end to see the grade? I think most of us as classroom teachers have a well-documented set of cases that say that skip-to-the-end is what happens, but are there times when it doesn't happen?
• I occasionally read comments (laments? bragging?) from teachers who say " . . . and then I added a full single-spaced page of comments at the end of the paper." I guess that's okay if it works for you, but I wonder if they're confusing quantity of comments with the effectiveness  of comments. Past a certain point of writing the end comment, it seems more effective to call the student in and talk with him or her than to keep writing.
• Given the way we've been trained by internet reading to look for short paragraphs, do the students even read long comments like that all the way through? Or if they could, would they write "tl;dr" and stop before you've been able to convey all those helpful hints?
• Another part of this invention: should we structure our comments like those ridiculous slideshows that are oddly compelling and force you to click through to see the whole thing? "Five Good and Bad Things about Emily's Paper: Click here to continue"? 
• Or should we maybe give them a chance to say "tl;dr" in comments to our comments?