An annoying problem arised when using x11vnc as a VNC server on one of my machines. Whenever I connected to it the Shift key did not appear to work from the client. For some people this is no problem because they have no notion about using capitals, but I do care. I tried two clients, both showing the same behavior, so I knew this was a server-side issue. Running xev (package xorg-tools) on the server showed me the desired behavior: the Shift key got captured after all. And Caps-Lock also just works.
The solution is using the -xkb flag when invoking x11vnc (or simply add the line xkb to your ~/.x11vncrc). It enables another (more powerful method) of matching different keyboard layouts, by means of an Xorg extension.