There is at Paranal an optical system (MASCOT details at: http://www.eso.org/sci/facilities/paranal/instruments/mascot/ ), used only at night time. This started as
a student project and is a relatively cheap commercial system. Full moon images do not look that bad, actually better than the ones without moon to spot clouds. Obviously is not working during the day.

The system is sometimes used in visitor mode to spot clouds coming in. Although there was a plan to
use the images to try and derive extinction measurements this has not been implemented so far.
The common wisdom (although it is not clear to me whether this is based on a real scientific analysis) is
that "when you see something in the cloud monitor you are going to collect bad data in any case".

The system is not used for scheduling and is not integrated in the environmental condition monitor.
All images are nevertheless stored in the archive and are in principle available for use.