Have an option and one keybinding to remove some or all of the U.I depending on the option you tick on the options menu. Example of removal options would include:
- toggle health bar/shield bar/picture [on/off]
- toggle item belt [on/off]
Depending on what option(s) you tick, one press of the keybinding will toggle visibility.
credit: http://forums.spiralknights.com/en/node/78235
poster:Bulby
To be honest, I didn't even know this was suggested before until someone posted there and brought it to the first page.
Like a screen shot mode? Simple but potentially useful option, I'm on board with that.