how could I re-map the 'Super' (left) key to launch an app? I want to launch Synapse with it, which is far more responsive than the Unity launcher. Cheers.
The 'Super' button can be set as an activation key in the configuration file for Synapse.
See Can I change Synapse shortcut to Super/Windows key alone?
xmodmap -e "remove mod4 = Super_L"might be in order to stop it from being recognized as a modifier. Your point about the OP wanting to unbind the Unity launcher from Super_L is very valid, though and I didn't take it into account. Also you're right about adding complexity typically not being a good thing.
.xbindkeyrcand that didn't work... Could you tell me how you got it working? Also the
xmodmap -e "remove mod4 = Super_L"didn't seem to do anything. I'm very interested in solutions to this question, if you have some time could you have a look at my question about Ubuntu key bindings in general (unanswered)?