I was at a seminar the other day, and during one of the...shall we say, less illuminating segments, I started reworking the B/X Thief in my notebook.
I think the whole x-in-6 thing, a la Flame Princess, might be the way to go. A lot of people who complain about the thief bring up the pretty legit point that many of his abilities have a 5-10% chance of working. Of course, AD&D and further iterations of the game would mitigate those low scores somewhat, but I think the Thief needs some love at the B/X or Cyclopedic level.
Okay, so here's what I'm thinking:
-At level 1, thieves get Pick Pockets, Open Locks, Find/Remove Traps, Move Silently, Hide in Shadows, Climb Walls, and Hear Noise all at 1-in-6. They get three points to spend, each point raising the chance by 1-in-6. (So spend 1 point on, say, Open Locks and he's got it at 2-in-6.) The thief may spend these points however he wants.
At 2nd level, and every level thereafter, the thief receives 2 points to spend. These points are restricted, however, in that the thief may not spend them on the same skill for the same level. A skill may not improve past 5-in-6.
At 4th level, the thief learns to Read Languages at 1-in-6. This can be raised immediately with one of the thief's 4th level points. If the DM doesn't really dig thieves reading languages, feel free to start it at 0-in-6.
Backstab and read scrolls work as written. If you're one of those symmetry loving folk, consider making read scrolls a skill and starting it off at 5-in-6, so that you're doing d6's for everything. I know it's not exactly equivalent probability-wise, but it's damn close enough.
Oh, one optional consideration for backstab...I liked Hackmaster 4th edition's take on backstab, which adds extra damage dice to the attack rather than a multiplier. x2 becomes +1 die, x3 becomes +2, and so on... the die matches the weapon type, so instead of getting double damage with a dagger, the thief rolls 2d4.
This has probably been done somewhere by someone, but I'm just throwing it out there.