Details are important...

I was struggling with this issue for 2 laptops in a row now... when I install the closed source nvidia drivers I get a GDM login window with extremely large fonts. I finally wanted to get of rid of this and after some googling, I found this: http://ubuntuforums.org/showthread.php?t=294429

Just add the following line to the monitor section of your /etc/X11/xorg.conf file:

Option "DPI" "96 x 96"

The DPI size of 96 pixels was enough for my resolution of 1900x1200.