where L is his or her experience level. Even an initially clumsy rogue with DEX of 8 or less has a SAS of (13+L), since training can do a lot to overcome biology! (In many flavors of D&D, a thief's chances at success don't depend on DEX at all!) The chances of success for a Very Difficult (5d6) or Arduous (6d6) task have a similar level progression as do many thief skills in, say, 1st edition AD&D.
But what about all the recent raking, bumping, and probing? Are there ways to take a one-roll system like this and flavor it up a bit without too much extra complication? I think so. If the resolution roll is a success, then all is hunky dory. But if it's a failure, then that's where the fun begins. In Homebrew '82, a rogue must first tell the GM how much time and/or care is being expended with any given attempt. A 20-minute patient bit of tinkering will likely have a different failure-outcome than a reckless, 10-second try! So, if the attempt fails, roll 1d6 on the FF table (Finessing a Failure? Forestalling a Fiasco? Fineousing a Fingers?) and use the relevant row:
For disarming a trap, + means a brief moment of worry where the trap looks like it's about to spring, but it jams and everyone is safe. 0 means the trap is sprung slowly, with lots of creaking or other advance warning noises, and it generally does half damage to anyone in its range. X means it springs, and full damage is done.
For picking a lock, + means the lock stiffens (and can be loosened with oil), but it can be tried again. If one more try fails, though, it jams permanently. 0 means the rogue just can't figure this one out -- but if the rogue levels up, or successfully picks another similar lock, then they can have another crack at this one. X means the lock jams permanently.
Of course, if the players have knowledge of this table, then it's the GM's duty to still mix things up a bit with some evocative, tension-filled descriptions and occasional outcomes that are outside the strict bounds of the above interpretations. Maybe a lock-picker gets a few hit points of damage on an X. Maybe that poison gas trap still spews out a little something even on a result of +.
I'm also wondering if this can be used with other non-mechanical skills. Two others that may be relevant are: putting on a disguise, and preparing a dose of poison (i.e., they benefit from more prep-time and finesse).
Anyway, this is all completely untested, so do with it what thou wilt.... :-)