I've been lucky enough to be using the beta of Live Messenger for a while, and I have to be honest, I really wouldn't want to go back to an older version. To put it simply, this is more than just another version of messenger. With Windows Live Messenger, users have a service that goes beyond basic text IM by helping them connect and share with voice, video and more. Features such as full screen voice and video calling, Windows Live Messenger enabled phone handsets, Sharing folders and Live Contacts to name but a few. I was using my laptop the other night when an old-sounding telephone ring started coming from my speakers - a colleague from France was calling me through Live Messenger. Having used other VoIP software products before, I was instantly sceptical, but upon picking up, all scepticism disappeared. The quality was exceptional, no lag, clear sound - and it was free! Try it for yourself! I've also used the shared folders, again, an excellent inclusion, and very useful.
Some of the less-major features, but little things I find useful include offline messages, so I can leave a message for someone when they next log on, and also the way that messages are grouped together into conversation pieces. Little things, but they make a difference.
You can find out more information here and you can download the new Windows Live Messenger here.
Try it, you might just like it!