Microsoft recently released a beta version of Messenger 2010/2011 (Wave 4). Although Messenger Plus! is not compatible with the new version yet, this new release properly detects the beta and do some basic initialisation for things like the auto-update feature.
When the new Messenger beta is detected, Messenger Plus! adds its usual "Software not loaded" menu in the contact list. From this menu, the compatibility window can be displayed to display some information and, more importantly, to let more advanced users disable "safe mode".
-- When safe mode is disabled with the beta, Messenger Plus! activates some of its functionalities. Using Messenger Plus! in this mode may cause all sorts of errors to occur, no support will be given for beta versions of Messenger.
-- If you experience issues after disabling safe mode, use the Maintenance wizard (available from the uninstaller) to revert Messenger Plus! to its normal state.
The Repair Wizard of the uninstaller now resets the "safe mode" setting of Messenger Plus! even if user preferences are not erased.
Messenger Lock and Event Logger work, those are the only relevant features (imo) that I have seen working. Chat history, text formatting, etc, etc. are not working.