In Scotland, it is a very common practice (probably in 50% of children nowadays, judging by the birth announcements - it's reached a real peak) to give the firstborn child, and in some cases all the children, their mother's maiden name as a middle name. But it's always a middle name. I like that.
I wouldn't do that for a first name, though. It'd seem almost as if the child had no first name - just a joining of the two surnames, if that makes sense.
At any rate, I prefer
Mackenzie on a boy, only because it's being done to death on girls across the Atlantic just now. The trendier parts of England (i.e.
London) are having a Celtic kick as well, giving their children Irish and Scottish surnames such as
Finnegan for first names.