When I run a java swing application, the metal look and feel is detected as the default one. My swing.properties file looks like this:
me@pc:~$ cat /etc/java-7-openjdk/swing.properties 
# uncomment to set the default look and feel to GTK
Back at the time I used Gnome2 in Ubuntu 10.10, it just worked. Now since I upgraded to Xubuntu 12.04 it doesn't work anymore.
I really want to change it, because I think the metal look and feel is really ugly.