The availability picker on Lion (when it even works) only shows the binary status with your busy times blocked.

The CalDAV request to show busy times just shows that you are busy, not why.

If you don't share private events (or keep that secure with a password to subscribe), your event details are as secure as anything on a web server with controls before you can retrieve the data. (not perfect security, but not wide open to anyone)

One person sharing two or more Macs, all running Lion

Method A: physical share of a disk

For your file to be versioned, save first to removable media with a file system that supports permanent version storage. Save all versions of the file to that volume.

Eject/unmount the volume. Use the volume with other Macs running Lion.

Examples:

• a USB flash drive using MS-DOS (FAT) lacks support
• a USB flash drive using JHFS+ does support permanent version storage.

Method B: electronic file share of a disk image

In a directory that is shared using Apple Filing Protocol (or any other appropriate distributed file system), create a disk image, maybe a sparse bundle. Choose a format — a file system — that supports permanent version storage.

Open the image.

For your file to be versioned, save first to the volume that is imaged. Save all versions of the file to that volume.

Eject/unmount the volume.

At another Mac running Lion:

• connect to the file server
• open the image.

Hints

The Secrets preference pane can help you to enable advanced image options in Disk Utility.

An image of a volume may be not reliably backed up whilst the volume is attached/mounted. For reliability, unmount/eject the volume before backing up.

Multiple users

Either method A or B will work, but both require negotiation between humans :-)

Method C

For each version that you wish to share, use the Duplicate command then save a separate file.

The downside of this traditional approach is separation. Users of other Macs (not necessarily running Lion) might take a Cover Flow view of the files, but that's not as neat as a versions browser view of a single file.

AFP, Apple versions and security/privacy

You might wonder why saving to an Apple-oriented file service, for example a service using Apple Filing Protocol, does not save Apple versions on the server. Think: privacy, security.

Example

Someone in Government saves a file that describes the true state of the economy, a state that is terrible. The person changes the file to present a different truth, a truth that will keep the lions at bay, saves his or her changes.

When ready to share, the author puts the one file on an AFP server.

Other users of the server open the file in any application that supports Apple versions. They see only one version, the most recent.

We (other users) might wish to see all versions of a file — including versions that were not intended for sharing — but for Mac OS X 10.7 (Build 11A511) the sanest default is:

• share nothing other than the most recent version.