Hey is there an application that runs down the battery on your ibook/powerbook so the battery calibrates. I always find myself not able to calibrate in the night to charge the computer back up because I still have about 30 % left and im dead tired.
I don't know about an app specifically designed for flattening the battery but I find playing a CD through iTunes usually does the trick. Pick something calm and it'll get you off to sleep nicely too, although it won't tuck you in...