Microsoft has opened the Windows Live Messenger Preview Site to the public
Windows Live Reviewer's Guide
Described as the “most meaningful way to stay in touch with the people that matter most and has great new ways to connect and share.” Microsoft is touting that this version of messenger is easier to use and has more meaningful interactions, keeps the best of your social networks at your fingertips and goes with you on the web and your mobile phone.
Microsoft has also built in better integration with Facebook, tabbed Messenger windows and video messages. Microsoft is expected to release a private beta version of Windows Live Wave 4 in mid May with a public beta scheduled for June.