Last summer I was looking for an instant messaging product to use internally at work. I had a go at setting up a Jabber server and although I got it working, it was hard work and I felt too messy to roll out.
We've since been testing Microsoft Live Communications Server and Windows Messenger. This works well but is a commercial product and will cost a lot to licence. Also since we upgraded the firmware on our firewalls it has stopped working across our sites and the firewall is complaining of SIP errors (don't ask!)
I've now looked at Jabber again and it has progressem immensely in the year since my last look. There is now a decent open source Jabber server called Jive Messenger and lots of jabber clients. I got the server up and running in abour 10 minutes. I then spent a large chunk of the weekend testing different clients and settings and finally felt confident to get a few people using it this week.
There are a few minor niggles but nothing major and I love the price.. free! :-)