I shouldn't say "improving", as font settings are very subjective. However, compared to Windows and OS X, the default font settings in most recent Debian-based Linux distros (such as Ubuntu) just look wrong to me. I've found two main reasons for this:
On the dpi front, Windows defaults to 96 dpi instead of 100 dpi, which seems to be where many fonts look their best. To change the dpi on Debian-based Xorg configs, edit the file /etc/X11/xinit/xserverrc and change the exec line to read:
exec /usr/bin/X11/X -dpi 96 -nolisten tcp
As for Freetype hinting, there are two font hinting options available: "native" and "autohinter." I'm pretty confused as to why there are two options, but it appears to be patent-related (see http://www.freetype.org/). In any case, I think that the "autohinter" setting looks much nicer. To change it in a Debian-based distro, run:
dpkg-reconfigure fontconfig-config
Follow the prompts to choose "autohinter", "automatic" subpixel rendering, and "no" to default bitmapped fonts.
After making the above changes, restart X (ctrl-alt-backspace).
Here is a before and after screen cap of the Xfce menu, with subpixel rendering off. Notice the lowercase "m" in the examples. And believe me, the "after" results look superb on a good LCD screen with subpixel rendering.
Note 1: Gnome and KDE both override the dpi setting in Xorg. Despite setting Gnome to use 96 dpi, the fonts still look wrong (using my lowercase "m" test).
Note 2: Be sure to play with the hinting level. You can usually adjust this in your window manager. I set the hinting level to "full".
I just upgraded to Ubuntu 7.04 and the font problem is gone.
