It looks like the info we gave you last week is correct as Mess.be have confirmed that a public beta of Windows Live Messenger 8.1 will be released tonight.

The build is due to be released on ideas.live.com sometime today/tomorrow (depending on you location, this evening if you are in the US).

It is unknown whether more new features will be in this build but it should contain the features that have been in previous 8.1 beta builds:
Improved compatibility for Vista
New/improved winks and emoticons etc menus
New personal status message options (specify your location)
New contact card design
New branding platform
Better re-authentication at sign in
Roaming display pictures (your current DP is used where-ever you sign in)
New platform architecture in important areas such as automatic updates and object store (where your personalised data is kept on your computer)
A sign-out option in the status menu
Appearing offline no longer forces you to close your conversation window
Quicker to sign into Messenger (8-15 seconds, compared to 15-25 seconds before)
New 'Frequently used display pictures' menu

Source: Mess.be (unfortunately we can't link you directly to the news post due to limitation in the Mess.be system/coding)

UPDATE: Will the "release" go ahead? Nobody seems to really know after Lapytsh, one of the first sites to report the release date of the public beta, have been told that it may not go ahead. It seems like another dodgy release date from Microsoft that has not been kept, but all of that can still change, or change again. Whenever it is released (if it is!) then we will be sure to tell you.

Lapytsh news post (via Google translator)