I think they do serve a purpose, as they intimidate the player trying to keep it on the inside of the dogleg. It also makes the drive even more intimidating because there is a stream on the other side of the fairway, which has caught many a contender on sunday.
however, I was up at the memorial today and Phil hit it all the way over the bunkers, leaving himself about 75-100 yards in. So, i guess they do serve a purpose, but aside from the longest hitters, those last bunkers really dont come in play.
Nevertheless, I think they course is fantastic from the couple times that I have played there. 14 is an excellent hole, and the greens are also fantastic.