Jabber IM has been great for our office. My company had previously used a corporate version of Microsoft Instant Messenger, but we got bought by a larger company and new bosses killed it. So, I did a little digging and ended up recommending that we use a jabber client/server as our local replacement. It works great! We’re using the Wildfire server and Spark/Gaim clients. Serves a software development group of about 80 folks.