Beta is the new passé, and dogfood is where its at. Calendar and now WebMessenger are now both in dogfoods that are running on external urls (you have to be signed up to the internal dogfoods in order to load the products - ie you need to be a Microsoft employee).
Judging from the screenshot it seems like Windows Live WebMessenger adds Personal Status Message integration, tabbed conversations (ok they are stacked vertically in a "conversation workspace") and display picture options, though those are already available from most Wave 2 Windows Live services, such as Spaces.
Unfortunately it sounds like the WebMessenger team is actually doing worse than the Calendar team, so don't get your hopes up for a beta anytime soon. Hey, at least its in the works though.
Microsoft, Windows Live, Live Calendar, Live WebMessenger, Messenger, WebMessenger, Beta, dogfood