You could read through http://training.apple.com/pdf/WP_FileVault2.pdf for some of the details, or `man pmset`. Use `pmset -g` at any time to see your current settings.

Just make sure you eject any removable disks before hibernating. And, sleepfast may drain your battery faster than the default hybrid sleep

OP said sleepfast increases his battery life. It sounds like you lose whatever is in memory though