Moq is not dead, it's heavily used and it has a steady download count both via nuget and google code. It's just that it works so great that there hasn't been any show-stopper issues that require urgent fixes :P.
vNext is coming along (a lot of spiking, throwing away ideas, etc.) slowly, and its new home will be in http://moq.codeplex.com eventually.
NuGet has somewhat changed the dynamic here, 'cause it's now much less friction to release new bits more often. We'll catch-up with more frequent releases soon. I'm just terribly busy with other stuff (opensource too some of it, heard of netfx.codeplex.com?).
Yes, Microsoft uses it a lot, as well as many others.
