[p_l]

Hurd failed not because of microkernel design, in 1994 multiple companies were shipping systems based on Mach kernel quite succesfully.

According to some people I've met who claimed to witness things (old AI Lab peeps) the failure started with initial project management and when Linux offered alternative GPLed kernel to use, that was enough to bring the effort even more to halt.

[RainyDayTmrw]

Most famously these days, Mac OS (formerly known as Mac OS X, to distinguish it from all of the earlier ones) is built on top of Darwin/XNU, which descends from Mach.