Mathematica 10 is not high-DPI-aware on Windows and so Windows renders it at the native resolution and then scales it by a factor of 2 by default to make it readable. Once Mathematica supports high-DPI displays in Windows, they will be able to properly render text and graphics that aren't blurry.
If you're running Windows 8.1, you can disable this default scaling of 2 for the application by right clicking on the Mathematica shortcut and going to "Properties" and then the "Compatibility" tab and check the box "Disable display scaling on high DPI settings." Once you do this and restart Mathematica, everything will be tiny but crisp and not blurry.
You can zoom by a factor of 2 by executing:
In:= SetOptions[$FrontEnd, Magnification -> 2]
Doing the above will result in crisp plots and fonts that are a readable size and it should save between sessions and between notebooks. It's not nearly as nice as native awareness of high-DPI settings that Wolfram could implement, but it's a stopgap. It doesn't apply universally, so help windows are a bit of an nuisance etc.