I used to fudge rolls to keep players alive but because I rolled in the open they knew when I was doing it. They told me it ruined the excitement of the game knowing that I would never kill them except by player stupidity and since my group at that time were fairly methodical players they were basically immortal. So I told them I would stop fudging, I did, and everyone had a better time. YMMV

As a side note I find that not fudging makes it more fun for me as a GM as well. It's no fun when you know the outcome before you start as a player and it's doubly so as a GM. It's fun when the players make you stay on your toes by rolling so well you have to alter the story. Sure the campaign plot may stay the same but how you thought the players would get there changes. Spices things up IMO.