> You could even TimeMachine-without-additional-drives... I mean, why should my snapshot system and my backup system be one? How about letting me use TimeMachine locally, and if I plug up an additional drive, TimeMachine asks me if I want to backup to it as well?

Unless something changes between now and RTM, Lion will provide that feature out of the box:

http://www.9to5mac.com/54117/time-machine-can-be-used-withou...

And that's about the only feature that a typical Mac user would benefit from with ZFS, without some kind of "prosumer" or "enterprise-y" external storage device.

I almost always use lzjb compression. It's nearly free and gives good returns for mixed data like the sort you'll find on system drives. Binaries, text, etc.

Also the reliability aspect. I haven't had HFS+ go bad on my own systems, but I've seen it several times on servers. It's on about the same level as ext3fs in that arena, which is pretty bad in my book.

I get the "less is more" argument and I agree generally. ZFS is so far beyond a traditional FS though.

One of the big reasons for Time Machine is to make it harder for Mac owners to lose data, either through hard drives failing, or user error. Backing up to the same drive only protects against user error. Instead of displaying a checklist of things you're protected against, Time Machine is an all-or-nothing deal, which makes the interface a lot simpler.

It also enables retail locations extra options to make users happier quicker: if a customer comes in pissed with a logic board problem that's the "third strike" for that computer, the support staff can simply ask if the customer has Time Machine backups, and send the customer away with a new-in-box computer without having to worry about moving drives around and migrating files in-store.

Apple's vertical enough that keeping Time Machine simple saves them employee hours around the world every day.

Lion actually makes local snapshots by default but the option to turn this on and off is quite hidden and even with local snapshots enabled the huge on/off switch for Time Machine in the preferences shows that Time Machine is turned off. All other Time Machine behavior is unchanged. This is, I think, quite a clever solution to the problems you were mentioning.

(This might still change before they release Lion, though.)

Lion does this by default.