The iCal standard includes a way to mark items as confirmed, so how about tying that in to an IM client, automatically setting the user’s status to Away or Busy if an event is confirmed by the user? This would cut out one step of the current “acknowledge alarm, set IM status, go to meeting” process by the acknowledgment of the meeting also serving as the trigger for changing IM presence status.

In addition to confirmation status, Away status could be set based on alarm settings, setting your status to Away/Busy/Occupied/Spacing Out.

If someone in your contact list (you probably wouldn’t want just anybody getting this information) attempts to contact you while you are away, your IM client could automatically send them event/appointment information:

Daniel will return from *event or location here* at 5:30pm (PST).

Or for multi-day events…

Daniel will return from Mars on Thursday at 5pm.

Using your local time zone (MST) is one display option. Automatically adjusting it to that of the person trying to contact you would be another.

For VoIP calls, appointment information text blurbs could be read aloud (using Text-to-Speech) to the person attempting to call you. Video conference attempts could also be handled this way.

Allowing users to specify when their status would be changed and optionally a custom away message when they first create a calendar event would allow more granular, independent control, but add to the front-end configuration and interface required.

For all I know, someone has implemented this – I’ve just never seen it. It might have even been among the GNOME Integration Bounties (working between Evolution and Gaim), but I can’t check due to the site being inaccessible at the moment.