Narcoleptic + Leonardo = Zzzzzzzzzzzzzzz
I love the Narcoleptic library http://code.google.com/p/narcoleptic/ for putting an Arduino into a low-power-consumption state for a period of time ranging from milliseconds to about a minute (per call to Narcoleptic.delay(); it takes a 16-bit ms arg).
HOWEVER, because it shuts EVERYTHING down, power-wise, if you have a USB-based AVR chip (e.g, ATMega32U4 as found on Leonardo and clones like the Beetle), calling Narcoleptic.delay(ms) ALSO shuts down all USB communication – including the communication needed to reprogram the chip. 
So, if you use this great library, I definitely recommend putting something like a plain old delay(5000) in your setup(), lest you find yourself slightly bricked. Recovery is of course possible, but it can be a PITA, depending on how hard it is to reach the reset button… and whether or not your board even has a reset button…
