Since I've upgraded my system to Ubuntu 11.10, Unity's global menu and search are having font rendering problems (no anti-aliasing, bad font sizes). No problem in sub-menus.
The font rendering problems do not appear on a newly created user. Just the ones which were existing before the upgrade.
What can I do to solve the rendering problems ?
You can adjust the font settings using gnome-tweak-tool 
. Do note that installing gnome-tweak-tool also installs gnome-shell.
To install gnome-tweak-tool, you can run the following command in a terminal:
sudo apt-get install gnome-tweak-tool
After installing it, open the tool and go to Fonts. The configurations that you should be changing are 'Hinting' and 'Antialiasing'.
Information about the options available:
The type of antialiasing to use when rendering fonts. Possible values are: "none" for no antialiasing, "grayscale" for standard grayscale antialiasing, and "rgba" for subpixel antialiasing (LCD screens only).
The type of hinting to use when rendering fonts. Possible values are: "none" for no hinting, "slight" for basic, "medium" for moderate, and "full" for maximum hinting (may cause distortion of letter forms).
I have found that to resolve this antialiasing problem you need to
rm ~/.config/dconf/user
In my case I had also lost the background and icons order, but it fixed after a reboot.
