Originally Posted by Katsunami
The Kindle DX is 1200 x 824 pixels at 9.7 inch, which makes 150 DPI.
The Kindle PW is 1024 x 758 pixels at 6 inch, which makes 212 DPI.
The pixels on the DX are bigger, so fonts that are the same size will look fatter on the DX, and thinner on the Paperwhite.
Look at a font that was made for older computer screens, such as Verdana. It was made to display well on screens such as 1024x768 at 15 and 17 inch, which comes down to 86 and 96 DPI. When you display it on the Paperwhite without fattening it up quite a bit, it looks spidery thin.
I use Verdana on a 1280x1024 at 19 inch LCD-monitor, which displays 79 DPI. This makes fonts quite fat indeed, which is good; for me. But now that there are newer fonts, and programs finally start to support upscaling (which was in Windows XP already...), I might look into a high-resolution monitor in the near future.
My desktop monitor is 19" (or is it 20") 4:3 1600x1200 resolution. Works very nicely for viewing fonts.