I think it looks all right for a boy, though I prefer it more for a girl.
If I ever get a chance to meet a boy/guy named
Willoughby, I would presume that:
1) His parents wanted a rare alternative to
William2) His parents liked the name when they were reminded of willow trees
3) He might have got it from the name of the place, surname of one of his parent's ancestors etc.
My PNL:
http://www.behindthename.com/pnl/149249