So this is what I did. I simply added gnome_enable="TRUE" in my /etc/rc.conf file. Now everything works just fine now.
Don't forget to include the following lines in the same order, namely:
dbus_enable="YES"
polkitd_enable="YES"
hald_enable="YES"
Also, in order to disable all that accounting stuff, I added the following line:
accounting_enable="NO"
When in doubt about these kind of aggravating issues a good place to visit is the web page at FreeBSD GNOME Project: GNOME 2.18 FAQ.
