I’m a long time user of Gajim for instant messaging. Jabber has the power and I can also use my (sigh) MSN account with transports. I have been using Gajim since version 0.7 and I’ve seen the number of its users increase a lot in these years.
Empathy is based on the Gossip GUI, but internally it uses the mighty Telepathy framework, that enables state-of-the-art messaging with most protocols. The interface is very simple to use, in perfect HIG style. It still lacks some features, but I prefer it to Pidgin, because it looks more clean and less cluttering. However, thanks to the very good work of the Pidgin developers, Empathy can use the Purple library to handle some protocols (most notably MSN) for which a native interface hasn’t been yet written, through the Telepathy Haze component.
Telepathy has a modular design, which makes it possible to develop the various components separately and even means more stable applications, because if a component crashes, the GUI application (Empathy in this case) can continue working. From an user point of view (that’s what I am), it’s a good piece of software. The working version of Empathy is still in Debian unstable, but it works without any problem.