Will I notice a difference?

[chexmixx23]

If I get a 19" monitor that is native at 1440x900 and change the resolution down to 1366x768 will I notice a big difference in how the screen/graphics look?

 

[anxiousinfusion]

At 19 inches, the 1440x900 pixel density is such that from within viewing distance anti aliasing will be required. You will be able to discern a drop in quality easily by setting your games to 1366x768.

Another thing to note is that 1440x900 is a 16:10 aspect ratio while 1366x768 is a 16:9 aspect ratio. Your games at that setting will look stretched top to bottom as a result.