For me the currently used presence messages bear the following meanings: Online = “I’m online, feel free to contact me! You’ll get an immediate reply.”, Offline = “I’m not available/the computer’s shut down”, Away = “I am online, but I haven’t interacted with my machine for a while, thus you’re not very likely to get an answer if you’re trying to contact me”, DnD = “I’m very busy atm, but you can leave me a message if you really really must”, Invisible = “I can see you, but you can’t! [You're some little voyeur, aren't you?]“.

I very much like the answering machine-like behaviour of queueing up messages in Away and DnD mode. This is very similar to the “Leave a message” functionality of the screen saver, which I see to be the physical analogue.

The second way of using status information is IMHO used to leave short messages to third parties (I see this happening esp. on Facebook). People use it to drop their friends a note about their whereabouts as well as exam results and favourite quotations of their current book.
As these two are IMHO to different aspects (the first providing you with information on how probable it is you’re replying to a message, the second being somewhat of a 21st century’s bill-board) of communicating with others through text, they should be made available to you separately.
Facebook does this the right way, though it lacks semantics (e.g. you could be studying ["Philipp is delving into databases"] but want to be reachable [status "Online"].

I therefore would love to have something that let’s me do the following:
“[Status icon/text saying "Leave me a message, I'll call you back."] Philipp is preparing greek salad. Yummie!”
“[Status icon/text saying "Give me some peace"] Philipp is doing his software architecture homework.”
“[Status icon/text saying "I'm bored, contact me! [did s.o. say "Skype me"?] Philipp is watching television”
“[Status icon/text saying "Offline/Not available"] “He who controls the past controls the future. He who controls the present controls the past. (1984)”"

And if this works with ICQ, Skype, Facebook, StudiVZ (German Facebook clone) and msn I’d be merry as a lark.

Finally some (quick and not very thought through) ideas about alerting the user (sound alone is not good as you may have turned that off): flash the screen (ah … may be annoying), slide in something (also annoying and not useful if your not fast enough), change background to a different picture (huh?), flash keyboard’s LEDs (no one would do that!), put sth. akin to a Post-it note on the user’s screen (remember “Leave comment”?).

Looking forward to see all of this to be integrated in the next Gnome release. Next goal: Booting in 1 second.

My computer is in the living room. When I’m not using my computer it will go idle. This doesn’t mean I’m not reachable. In fact, all of my family lives abroad and I would love for them to IM/skype me when I’m just hanging around in my living room.

That said, I never take the trouble to change my status manually anyway. I let it set my status automatically (offline, online, idle). Maybe I would use invisible or offline once every two months when I’m really really busy.

I have idle notification disabled in all my IM clients. I don’t really care to let people know how long it’s been since I’ve been at my computer. More importantly, I don’t always want other people to know that I’m definitively at my computer (by the fact that I’m *not* idle).

Many people treat the statuses a bit differently than intended. One friend of mine is ‘away’ 90% of the time she’s actually at her computer. Another (who uses the gmail chat interface) is ‘away’ when not using the browser, and ‘do not disturb’ almost always while chatting.

Personally, I’ll leave myself ‘away’ when I just don’t feel like letting people know I’ve returned to my computer just yet.

It’s basically just social pressure that makes people do most of this — if they’re at their computer, and their status is listed as ‘available’, they’ll feel guilty about ignoring messages from people if they don’t feel like talking. But if you’re listed as ‘away’, that changes everything.

Anyway, I wouldn’t think automating or removing some of these options would be a good idea. Giving the users the ability to remain ‘away’ while in conversations or the ability do disable idle time reporting are a must.

I’m also not sure I understand your beef with the ‘offline’ status. I can think of a bunch of reasons why you’d want the client running but left in an offline state, offline access to the chat log viewer, for one thing. I also might want to go offline for a while but leave a bunch of chat windows/tabs open, and not lose that state by closing and reopening the app.

Some of the more popular ones are: nickname,geoloc,tune,avatar,mood,activity

This means you do not have to hijack the status info for such things as many common IM applications do when interacting with legacy protocols

I have spoken with the empathy folks about this, and it turns out there is some rudimentary support within the telepathy-gabble codebase for this

This support is based on a subset of the of the Publish/Subscribe XEP
http://xmpp.org/extensions/xep-0060.html

XMPP also allows one to be “available” to some folks, and “invisible/hidden” to others, either on a group or individual basis.

There are of course even more precise ways of handling presence/messages to some folks that involve implementing the privacy lists XEP
http://xmpp.org/extensions/xep-0016.html

I use an IM client on both my home and work machine, and I go “offline” whenever I am moving from one to the other. I could quit the program, but that’s a lot less convenient for me — there is some state lost there, like the window position and which workspace it was on. To me, this is like saying, “Why suspend your computer when you can just turn it off?” The answer is that it’s a hassle to get everything back.

Moreover, if you want presence to be an omnipresent part of the desktop there are necessarily times when you want to voluntarily be “off the grid”. If you can’t quit the app, you need some sort of offline mode.

When I am DND (or whatever you call the mode where messages don’t pop-up) it doesn’t matter what it’s called.

And I think everybody using the computer seriously is “busy” more or less all the time

So, online, busy (no messages/pop-ups/notifications), away from keyboard, and invisible (for damn busy, do not want to be disturbed at all, but people can still leave a message, is fine