I found several interesting "tidbits" in the March Readers Digest.
An interruption of only 3 seconds doubles the chances of making an error in any task involving a series of steps. It'd be interesting to test that theory.
Now - if you need to know when to caffeinate or nap - according to Vanessa Gregory - this is what you need to do:
If your head hurts - you should drink coffee because caffeine improves the absoprtion of pain relievers - so the combination of an aspirin and a cup of coffee will help your headache.
If you want to run faster - drink coffee - caffeine boosts your endurance and speed.
If you're grumpy and sleep-deprived - you should drink coffee and take a nap (what can be better than that!!)
If you need to ace a test - take an hour long nap - that is as effective as a night of sleep in terms of storing information.