Hmmmm, early days yet, but nothing "works" for me. :(
I have WLM 792 and YM 508, and can ADD any name I like to either (including made up fake names just as easily) - but I never get indication of anyone across network being "online" (even when I know they are).
And sending IM from YM... it "goes", but never reaches WLM.
Sending from WLM, it always just says your msg couldn't be delivered.