So I've been comparing my ipad3 to my ipad1 (I didn't get an ipad2 because I only wanted the higher density screen)
Back in 1999 I saw a technology demonstrator at IBM's Almaden facility in San Jose where they showed a 200 ppi LCD display. It blew me away. The scientist who worked on it talked about eye strain and how 200 ppi was the 'magic' spot where more thank 75% of the people stopped noticing the strain of making lines out of pixels.
So after unpacking my ipad3 one of the first things I did was to download the Economist app (my favorite btw) and bring up the latest issue on both the ipad1 and ipad3. Side by side the difference is very visible, absolutely can distinguish between the ipad1 and 3 with p < 0.01 :-) More interestingly comparing the ipad3 version to the print magazine its clear that the ipad3 is pretty much identical from my eyes perspective (disclaimer I do wear glasses, no 20/10 vision here).
Now if I could convince folks that send me catalogs to offer an ipad version I'll be in good shape.