A bunch of interesting assorted notes about Irish names. (Published in 2016.) (Link via Marguerite.)
A few hundred years ago people paid little attention to how names were spelled. One extreme example is on a tombstone in Ireland where the surname for a family of six is shown as McEneaney, McAneany, McAneny, McEnaney, McEneany—and Bird (from the mistaken belief that the name comes from éan, a bird).