This is by far the most helpful and entertaining review that I've ever read on Amazon. I also appreciate that you organized your comment into paragraphs, as well as using proper grammar and spelling. Where do you go to law school? They're obviously doing a good job. Seriously, thank you. If only Amazon had editors for the rest of the review monkeys...
Anyway, enough of my babble. Here is the information you requested:
The damage to the screen is caused by two factors:
(1) The height of the keys with the protector on top of them.
(2) The cleanliness of the protector.
Any real "damage" comes from people who are too lazy to clean their keyboard protector. Dust builds up on top of the silicone/polyurethane, and pushed into the screen. LCD screens should not have pressure on them over an extended period of time (i.e. when these people with dirty covers leave their computer closed every night for weeks on end).
You'll know if you have a problem if/when you see any resemblance of the outline of your keyboard on you screen when you open your laptop. Apple computers have a good resolution and particularly glossy screens, so you will be able to spot the dust patterns easily.
Don't panic, but rather just take your cover off, wash it with soap and warm water, and leave it to dry (use a hairdryer if you're impatient, or newspaper and/or a countertop if you aren't in a rush. Paper towels, bath towels, and tissues leave too much residue, defeating the purpose of cleaning).
Hope that helps!
P.S. Your infomercial-style testing need not occur (unless you get a free computer to test with!), since all of these keyboard protectors are basically waterproof... BUT, in the case of a spill, hold down the edges of the protector so that your Amateur doesn't become too wet, or caffeinated.