According to Wikipedia, it's happened 6 times in MLB history as noted below:
" This is only done in the rarest of cases, typically when the pitching team is leading by four runs or less late in the game and a particularly feared hitter is at the plate. The six players given such passes are Abner Dalrymple (1881), Nap Lajoie (1901), Del Bissonette (1928), Bill Nicholson (1944), Barry Bonds (1998), and Josh Hamilton (2008). In all six cases, the pitching team went on to win the game. "
I remember well the Barry Bonds one, it was amazing to watch and a testament to his fearsome prowess at the plate. IMO Leyland did exactly what he should have, pitched to Ortiz. It just so happens that our beloved Big Papi hurt them this time, further enshrining himself as one of my favorite Red Sox players of all time. Go Red Sox!!