Hmm so I actually had never come across this issue, but recently I've seen a few posts on various blogs about how people don't wash their faces in the morning, as they feel it's clean from the night before.  Now to me this is insanity!  When you sleep your face heals and recovers, and as such it is generally produces oils, and emits toxins from itself.  Your skin is the biggest organ of your body - it does a very good job of detoxifying itself, and as such, will get dirty, even with invisible dirt that you cannot see!  Not only that, but would you really want to put make-up on top of an unwashed face?  You would be literally trapping the oils and dirt under a layer of make-up!  Or let's think of it another way - just because you brush your teeth at night, and they are clean when you sleep, does that mean you'd even think about not brushing them in the morning?  For the most part, I think the answer is no - so give your skin the same respect as your teeth! And listen to the monkey. I know I do, I love monkeys=].
Love A.x