I can see this being real useful for 12 inch Powerbook users, or iBook users if they ever want to swap batteries. Since only the 15 and 17 inch Powerbooks allow battery swapping currently when in sleep mode, this at least gives Apples entire lineup the possibility of swapping now without losing work.

Desktops might find this handy if attached to a UPS. Enable it, and set the system to go to sleep when the UPS goes to battery power. That way even if the UPS dies, the system will still come right back from where it was.

I think Apple's decision to not seperate this into multiple things like Windows does shows their typical refined though process. Sure, Windows does hibernate. Sure, it does sleep, but you have to pick between them.

Here's the WHY: Put your powerbook to sleep. Something jars your battery lose, it goes dead, you forget to put another one back in (orjust don'tdo it quickly enough because your kid fell down the stairs (happened to me). When it's completely out of power, it switches to using the safe mode, and will restore from disk instead of being the equivalent of unpluggin your desktop while on.

Well, here's the problems with your examples. First, if you set it up to safe sleep after a period of time (like you do on windows, so it sleeps for 4 hours, then hibernates), then if the battery pops out in the first four hours, you're still screwed. If you're not 'sleeping' but the computer is on when the battery gets jarred, you lose power and all your work anyway. Of course, I'm basing this on my iBook, which, when won't let you swap a battery asleep or anything like that (maybe powerbooks can handle being asleep for a short time without battery, but doubt it would help if your computer was on and working).

the switching to safe sleep while sleeping only would work if your computer actually can track your battery well. My iBook sucks at this (I need a new battery, though). It goes from 100 to 75% then just goes to sleep without warning.

And it would be nicer if Apple could just enable this for all their computers, esp. if you have a desktop tied to a UPS, be nice not to lose your work if the power went out for more than a couple of seconds while you're off finding candles.

is save RAM to disk as soon as sleep mode is entered, and NOT after waiting until the battery is critically low. Then if the battery dies abruptly or gets removed the RAM data is ready & waiting on disk.

This is a really cool feature. Its real useful if your battery is low and the computer goes to sleep, and then the battery runs out even while asleep. Now instead of going through the bootup sequence, it just reloads the state that the Mac was in. I can't be the only one who has a bunch of email messages and web pages and other apps and docs open. Even if its saved, I still have to go back and open everything up and get everything back to how it was. That's a pain. Now I don't have to worry about it.

Oh, and for those who don't understand how it works(hint: read the article) This is the process:

1. Close lid or choose sleep from the menu. 2. The Mac automatically saves the entire contents of RAM to the HD. 3. It goes to sleep now like any other Mac. 4. If the battery power is lost, everything in RAM is lost. 5. When a power source is reconnected, and the Mac is started, it copies the state from the HD back into RAM. 6. The Mac than "wakes up" like any other Mac.

I have a Ti Powerbook (550mhz) not sure when it came out but you can switch the batteries in it during sleep mode, i just swap the batteries immediately during sleep and no problems happen.

According to apple's page:

"Prior to your system entering sleep, Safe Sleep automatically saves the contents of main memory—such as desktop settings, open applications, and other work in progress—to the hard drive."

What this sounds like is that it's not going from active, to sleeping, to hibernating. Instead it's making a disk snapshot when it sleeps, as a backup, and it only uses it if it fails to wake from sleep.

In many ways this is better than having a separate hibernate state, because even if the battery gets removed while you're in "sleep" mode... even if only seconds after going to sleep with a fully charged battery... it will recover.

It would be nice to have a mechanism to take this snapshot and then completely power off if you're not going to use your laptop for a few days, so that when it comes up again it'll return from Safe Sleep fully charged. I guess you could just sleep it and remove the battery, but that seems a bit of a kludge.