A few other tips...
disable AirPort and Bluetooth, they use power.
don't put a media in Combo/Superdrive unless needed.
don't plug in your iPod. (iPod will get charged from MacBook/MacBook Pro/iBook/PowerBook, even if they are running on battery.)
charge your batteries whenever and wherever you can, but remember not to do so in German railway stations. (we can't forget
Jan Michael Ihl's story)
If you are about to buy a new laptop, there's one factor to consider: MacBooks (iBooks) tend to have longer battery life than 15" or 17" MacBook Pro (PowerBook).
Antony, Happy Devil's Day.