How to Create Custom Hot key to Launch Applications in GNOME

1. Open Applications -> System -> Configuration Editor from the GUI

OR

Open a terminal, type gconf-editor

2. Go to "apps" -> "metacity" -> "keybinding_commands"
3. Double-click on an unused element e.g. "command_10"
4. Type in the name of the application you want to launch, for e.g. "firefox" or
"gnome-terminal"
5. Then go to "apps" -> "metacity" -> "global_keybindings"
6. Double-click on the command name that we have edited in "keybinding_commands" Section.
Here for me it is "run_command_10"
7. Then enter the Keyboard shortcut you would like to launch the application
I entered

"<"Alt">"t

here (without the quotes) for gnome-terminal.

Thats all

Go to Desktop and type Alt+t a GNOME terminal should open. It will depend on the active Windows also since some other applications may be having the same HotKey.