Windows Live Messenger 2011 was released
end September (beta was available since mid June - but a lot has changed internally since then). So, that is roughly 3 months since the public release till now. Also note that Windows Live Messenger was released way sooner than what was expected. The Messenger Plus! team has been working in overdrive since then...
Note that it is not just about making Plus! compatible by applying some tweaks, this is not just a simple update like previous versions were. And on top of that, there are a whole bunch of other things they need to do besides the software itself. It is a complete overhaul of the software, website, services, etc. And don't forget that the department responsible for Plus! (=the current team of programmers who _first_ had to learn how Plus! was made; they never worked on it before) was only founded in June or something too....
And then you may not forget everything must be tested and translated.
Considering all of this, they are doing a good job, and as fast as humanly possible.
Better a delayed product than a half-arsed rushed one.