If you have the monitors set up as 2 different displays (meaning not mirrored) then the displays are able to run independently. With that being said, it seems like I read somewhere that Apple displays have somewhere around a 110 dpi, where as monitors found on normal laptops and external monitors were around 96 dpi. This would cause the fuzziness that you are talking about also. A great way to tell this is drag something like a text document from the laptop display onto the external monitor. If the window is 6 inches long, it would be longer on the external, due to a lower dpi, even though the external monitor might have a higher resolution, the dots that make that resolution are not as close together. Hope this explains things well enough.