Originally posted by: velis
It's all a matter of DPI. If you have a 300 DPI display (non existant currently), you're very likely to not need any AA since the dots are small enough. Some people might still notice the jaggies upon close inpection, but that's about the resolution you need. Current displays however with their 100 DPI resolution have rather large pixels and so you notice the jaggies. So buying a 17" LCD will provide you with "smoother" picture than a 19" one because they both have the same res (1280x1024), but the 19" one has a lower DPI. The other thing you can do to help is move further away from the monitor. Your vision is not perfect and the further away you'll be, the smoother the image without AA will seem.
High DPI monitors on the other hand tend to have certain readability problems since no operating system currently available (AFAIK) has pure vector GUI. Your windows system font is only about 16 pixels high and it would be just as high (in pixels) on a high DPI monitor making it really hard to read dialogs. Switching to large fonts tends to do "wonders" to dialog layout

I know IBM is (was?) selling a 200DPI monitor (2560x1600 res, but on 19") for a few years now, but nobody really hyped that since it has the issues mentioned. Hope the next generation of operating systems fix this non-vector GUI issue so that monitors can start gaining on DPI.