One of the apps I really liked on OS X was Quicksilver. However I really only used a small subset of what it was capable of. Mostly I found using it as a smart ‘Run Dialog’ was quite handy.
To that end I decided that I would bind a run dialog to the same key combo as I had used with Quicksilver.
Nothing in Gnome is straight forward and it took a little digging, but I figured it out. To set up our custom keybinding (we’re going to use <ctrl>+<alt>+r to launch our run dialog) you have to install or already have ‘gconf-editor’.
Fire up gconf-editor which appears to be an ill-conceived regedit and navigate to
apps -> metacity -> global_keybindings

Double click on the run_command_1 and then hit the key combination you want to use. (In my case <ctrl>+<alt>+r).
Now, we need to map that combo to a keybinding_command. Click on ‘keybinding_commands’ (right below ‘global_keybindings’ in the left hand pane) and double click on ‘command_1′. Type the word ‘gmrun’. You’re done with that part so go ahead and close gconf-editor.

If you haven’t already done so, install gmrun. `sudo apt-get install gmrun`.
Now we are ready to give it a shot. Hit the key combination you picked for your keybinding, and when gmrun appears, start typing. It supports tab-completion, so you really only need to hit a few letters and then the tab key.

One more gmrun tip before I end this post. You can create a ~/.gmrunrc file and set up certain behaviors (see man gmrun for a full list). For example in my gmrunrc I set it up to make Firefox handle urls in a new tab:
# Url Handler
URL_http = firefox -remote "openURL(%u, new-tab)"
Happy computing!