I spend my day on laptop and thus hate to take my hands off keyboard for mouse or touchpad. I like launching and using programs from keyboard all the time. So i found Gnome Do which is a great tool, a lot of plugins to integrate into commonly used programs such as firefox, pidgin, evolution to increase productivity. There is also something like this in KDE, i think its called katapult.
Even when i shifted to mac some months ago to taste iphone development, i couldn’t live without it and used QuickSilver which is basically for the same purpose.
You can install it from add/remove, synaptic or apt-get by the name “gnome-do”. Make it run at startup by adding it to System > Preferences > Startup Applications and your life will become a lot easier.