I have no problem with automatic success/failure.
In the games I run, I do not tailor all the encounters for the PC's. Most are tailored, some are just random. A horde of kobolds? Yeah, the players know they will probably win. What's more, they will probably win pretty handily. But, they also know that even the lowliest kobold might get a lucky hit in. They also accept that a normally easy save might be bungled.
Oddly enough, the "unfairness" of it has never cropped up. If I can't think of a justification, my players usually can. There have been many, many times where a Fort DC 14 ghoul paralysis took down mid to high level Barbarians, Paladins, or Fighter/Clerics. The players do not like those natural 1's, but they think it makes the story interesting. They also don't mind when the creatures get that natural 1.
I had a mallebranche (Demon, most recently converted in the Monster Manual II) that was tasked with assassinating the fighter/cleric. It would typically do 50-60 points in that first round. Not enough to kill the PC, but easily enough to get some attention. In all 3 encounters with that mallebranche, the resolution was a dismissal manifested by the party Psion/Ghostbreaker. It was sad that all three times, that natural 1 came up and the mallebranche went away. It was also funny and became a running joke that the little telepathic Psion would tell the mallebranche to go home, and he would. Her unreal charisma would manifest in interesting ways.