I'm relatively new to XFCE. I would consider myself between an intermediate and advanced linux user. I'm using XFCE version 4.8.1.
At home I use AwesomeWM and have gotten used to pressing Mod4+Enter (<Super>+Enter/<Super>+Return) to open a new terminal.
At work, however, my system is a RHEL6 system and after many hours of failing to build AwesomeWM on the machine, I switched to XFCE (not a fan of gnome or KDE).
I am unable to bind <Super>+Enter to my terminal command. I was able to bind <Super>+t to the same command and it works just fine.
What happens when I try to bind <Super>+Enter to a command:
I go to Menu > Applications > Preferences > Keyboard > Shortcuts > Add New. I type in my command (in this case "urxvt256c -geometry 320x89+0+0"), click Next, and when it asks for my keyboard shortcut I do <Super>+Enter. Now "<Super>+Enter" appears on the dialog for a short time and then it seems to think I'm clicking the Cancel button.
So I tried to edit my ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-keyboard-shortcuts.xml file, killed xfconfd afterwards. It is now showing up in my Keyboard Shortcuts GUI, but the shortcut itself is still not working (note: Super+t still works fine).
I'm at a loss. Is it safe to say this just isn't a binding that XFCE will accept?
Old post, but anyway: you could try installing xbindkeys, it should allow you to bind any key combination to any arbitrary command.