It's very easy to set is for a session. Open terminal, go to Edit --> Current Profile --> Title and Command and tick the "Run command as a login shell" box.
Problem is, you have to do it every time you log in. Your first terminal never gets to see your environmental settings. We need permanent solution. Searched and googled, googled and searched. Found a wealth of information on the Red Hat site.
They definitely put me on the right track (and convinced me that I do need to learn xml after all!). However, the article omitted to mention one important bit of information. When you change the settings with the gconftool-2, you must stop the gconfd-2 daemon. I didn't, and had all sorts of desktop problems, including Nautilus crash.
So, to make every gnome-terminal a login shell (e.i. read your environmental files) first stop the gconfd-2 process. There may be a clean way of doing this in runlevel 5, I chose to go to runlevel 3, which is a full multi-user mode of operation, but without X (GUI).
Do the following steps only if you *don't* have any applications or users requiring GUI - you risk P45 or your tyres slashed otherwise.
Log in as root and enter:
# init 3
Press Enter (after few messages) - that will show the prompt again. Enter:
# gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.defaults --type boolean --set /apps/gnome-terminal/profiles/Default/login_shell true
Return to GUI runlevel:
# init 5
From now on, every user's terminal will source their startup files...