Skype seems to work just like the normal Phone app. Watch the demo starting 22:25 (http://events.apple.com.edgesuite.net/1004fk8d5gt/event/)

My point about skype was not that it cannot be backgrounded, but as I said "skype will be integrated in a way that it takes your desktop space". Not sure what happens when you have more accounts - if you can do that at all and if it continues adding new bars... but I prefer it completely invisible like in N900 (especially when I have 2 voip accounts and 3 more voice-capable xmpp accounts online)

I doesn’t take anything. The double high status bar is a standard UI convention of iPhone OS. It appears when something requires your interaction and is in the background (like ending the call or stopping the voice recording).

Ah, I think you may be right about IRC. Apple continues to want such things to be done via Push Notifications. Which is a pretty good solution for most things, though not all. E.g. I do IM (Windows Live) via Meebo, an app that uses notifications, and don't have any problems with it. IRC seems like it could work pretty well through such a system, too, though I don't know if anybody offers that service.

They specifically showed Skype as being able to run (continue calls or receive new ones) in the background through a very similar UI to the current built-in "Phone" app, so I think you'd be good on that one.