This hint applies if you have GTK applications installed through MacPorts. It may also work with GTK applications installed through other means, but your mileage may vary. These applications, by default, look really ugly because there's no decent gtk2 theme engine installed. But it's actually very simple to install one. In Terminal, just type:
port search gtk2
Some gtk2 packages will be displayed, but we're interested specifically in the gtk2 theme engines, such as gtk2-aurora and gtk2-clearlooks. To install one (I highly recommend one of those two), simply type:
sudo port install gtk2-aurora
You will need to enter your administrative password for sudo.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080309171359879