Leslie (for a boy) is an old name but so far, I haven't seen any signs of a revival. The only one I knew was my uncle, born 1917. The shortened 'Les' always makes me think of a rather seedy man coming out of a betting-shop!
Leslie (Scottish spelling)//Lesley (for a girl) again, I haven't seen for ages. I suppose the shortened 'Les' for a girl might lend itself to all sorts of less-than-complementary names!!