Messenger Plus! is a freeware program that uses API to add many useful features to MSN Messenger. It has built a strong reputation over the years and is used by many (such as the Neowin Admins), who are in the know about software.
However, with the leak of MSN Messenger 6, the future of Messenger Plus! has been put in doubt, because instant message windows no longer use the standard controls, which are currently essential for plus to work.
Messenger Plus! Creator, Patchou, says "I"m also 100% sure that Microsoft removed plus! support on purpose. It"s not just "we updated and oh, too bad, your software can"t work anymore".... they did some things especially to avoid Plus! to function".
Another concern put forward by the MSN Messenger Community is that MSN has stolen one of the most popular features of Plus!, Chat Logging. Although it"s great that it"s now a standard feature, it"s not-so-great that they are making it hard for Plus! to continue it"s development.
Plus! is currently working on a solution for this; when MSN Messenger 5 was released there were some changes which required a few changes to the Plus! code.