Seth Goodman wrote:
And, just to make things interesting - some friends of mine have one
of
those single-handled shutoff valves on their washer - and were very
good
about always remembering to keep it closed when not using the washer.

One day they came home to find a flood in their laundry room - the
valve *itself* had failed. The valve looked like this one:
http://www.plumbingsupply.com/images/washvalv.jpg

Note the two large screws at the top of the valve - one of those
screws
blew out, causing the flood.

Fail-safe mechanisms always fail by failing to fail-safe.