For those of you who travel great distances OR like your laptop to sleep instantly OR want to save disk space equal to the amount of RAM you have installed (great for us MBA users)...

I haven't been using this for long, but as a MacBook Air (SSD) user, I love the ability to reclaim 2GB of precious disk space :)

Here's how I use it:

1) Install for all users (otherwise you don't seem to get the options).
2) In System Preferences, choose "sleep only" and then delete the sleep image (saves me 2GB of disk space).
3) Choose "smart sleep". This will ensure that it only hibernates (i.e. writes RAM to disk) if your battery is below a certain level.
4) If you are on a long-haul flight (e.g. Aus to UK or LA), choose "hibernate only". This will always write everything to disk and will turn the machine off. When you open your laptop, it will take a while to copy from disk back to RAM. I find this mode saves the gradual drain of battery power that occurs when in normal sleep mode.

If you have a laptop with that occasional "fail to wake from sleep" problem, then I suggest you don't use this tool. On the rare occasion when the laptop fails to wake from sleep, you won't be able to retrieve your sleep state using the "remove battery" trick which forces the laptop to restore the sleep state from disk.