If you do a lot of terminal related work, running applications and doing multiple ssh logins and you dont like waiting for a couple of seconds after clicking the gnome-terminal. More importantly if you had been a Quake player in your childhood, you are going to love
guake. Guake is a fast quake style terminal which comes up and goes off in the background with F12.
In ubuntu you can install it simply by
sudo aptitude install guake