I think it's cool, but honestly only because of
Luna Lovegood. :)
I don't know anyone named
Luna, though I do know a girl whose surname is
Luna. Loona is actually cool because it makes me think of loons, but I don't think it would be a great idea to use because it's also close to looney.
It has the sound of a name that could become more common, but I think it's too hippie/naturey to really get that popular.