Well, they gave a good college try at interfacing with existing social networks. When Windows Phone 7 launched, the MS web/mobile infrastructure had fantastic interoperation with FB and Twitter - FB messenger was even their official supporty IM (kind of a snub to MSN Messenger or whatever it's called isn't it?) Then they bought skype and APIs shifted and things fell apart, but for a while it was really neat.

I'm not surprised to see MS say "screw it" and just buy their own.