HN user
Also the complete opposite of my experience. I used the nightly builds almost exclusively for over a week on Ubuntu 9.04 and I had no performance issues. Things are certainly incomplete but I was slightly disappointed to go back to the poorer performance of Firefox. I should probably place that blame on the Flash plugin but I think Chrome will handle this problem much better.
It's not an interview, rather a book excerpt, and was published two years before the link you provided.
I'm not from the UK and I don't know anything about this but it appears this should be sims.co.uk
For IM, XMPP would be a wise choice. SIP could be be used as part of your voice/video solution but they are different things and as such you wouldn't choose one over the other unless you were choosing IM over voice/video.
Google chose XMPP and developed Jingle as an extension to allow for voice/video.
You could just build your setup on Google's services and take advantage of Google Apps for your domain.
Also, notice that they have not updated libjingle in over 2 years. They should include some sort of statement about the status of the project. It's my understanding that it won't even compile without work but I could be wrong there.