We are only just starting to see higher ppis in bigger devices (retina macbooks, high ppi tablets, limited ultrabooks).

But even the difference between a 13" laptop and 15" laptop is noticeably crisper when directly compared at the same resolution (1366x768 in recent years).

Even going from an older 1680x1050 22" monitor to a 16:9 1920x1080 is a somewhat noticeable difference.

However when you aren't comparing directly, or switching from one to the other, it is hard to see the clarity improvement.

Looking at a 22" monitor from a retina display makes the fonts look blurry and off but if you start working on that monitor at the beginning of the day it isn't quite so bad.