I certainly don't want to rehash some of the arguments about it, because I wasn't a fan of them at the time...but I was referring to the context switch penalty of running multiple system level services is separate processes.

Mind you, I've always thought that argument was specious for several reasons...but in a naive implementation breaking a kernel unto multiple processes would have to have higher context switch overhead.

I've always though, though, that not everything needs to be process isolated, and using more of a message pass system could probably overcome context switch overhead in multiprocessor system's

EDIT: GOD DAAMN PHONE. I think that the reliability gains may more than make up for any perf problems.