I've got two friends from the local cycling club who DNF'd PBP back in 2003. One of them is definitely trying to do all of the qualifiers to get back and take care of "unfinished business," the other is going to ride his bike across the US this summer. Some of the other folks in our club have also finished it, but if you ever ask them about their experiences they'll all give you the 1000 yard stare.
Randonneurs are a different breed, I tell ya'. My hat is off to them, but there's no way I could do it - my booty couldn't stand it.