After upgrading to 13.04, the first thing I noticed was that the neat window title font (and all the other default system fonts I'd enjoyed) were replaced with other fonts. Also, the terminal font has really messed up spacing and is definitely not the font it's supposed to be. I checked the system settings, and even Tweak said the fonts weren't serif....why is this? (Tried uninstalling Tweak; now the "Appearance/Behavior" settings group isn't even available.)
See if this applies to your case. It fixed the font spacing problems I was having in Gnome Terminal and Gvim.
I used Syanptic to determine the unidentified library. The following cleared it up for me.
$ sudo apt-get purge libpango1.0-common pango-graphite