I really like the elegance of the idea of using roll d6 to determine skill-like tasks, as in B/X with 1-in-6 chances of finding secret doors and so on (good post here ). But in practice I have problems with my players not really understanding it. I certainly can't rely on them during the game to understand and be fluent with them even when they're on the character sheet, like when we've played Lamentations of the Flame Princess.
To deal with this, in the rules I actually use, it's just attack roll style for all skill checks - roll d20, add ability scores + a bonus for "skills" (PCs get 2, rogues more). Although that's the compromise I've come to when actually running a game, I'd like to use LOTFP or B/X style 'skills' again (for B/X, rogue/thief skills converted to X-in-6 probability ala LOTFP). To fix the problem with it being counter-intuitive players, however, I'd keep these DM rolls. I wouldn't mind explaining, and would roll in the open, but I'd rely on the PC to describe the action and then simply roll the check myself. A more "fiction focused" way of doing skills if you will. I like something about the simplicity and straight-forwardness of the d6 skills, while I like how in LOTFP they increase with level. I think I also like there being a set list of skills. The universal mechanic of using the save for skills keeps everything consistent, but it lacks the soul of some set skill checks - I feel like PCs are just so much more likely to ignore explaining what their PCs are doing and saying "I make a stealth check."
One question I'd have, though, is whether to add ability score bonuses. My inclination is to use them. I like how a usual 1-in-6 break down doors type check quite naturally flows into adding a STR bonus, so a strong character has a 3 or 4 in 6 chance with the door. It reinforces the importance of ability scores. You could add INT bonuses to search checks or whatever, making that an important ability for non-wizards too. Another variation, to go with the more DM-facing check, is that then you can have circumstances in which you add the score bonus and circumstances you don't - maybe adding DEX to Stealth checks if unburdened and not wearing armor or something. Likewise, adding +1/+2 for smart PC preparation or appropriate equipment. If I did this, I'd have to ensure NPC/monster checks are similarly competent, which is a downside that removes some of the elegant simplicity of the d6 system.
Obviously, the d6 skill system works, we've got plenty of playtesting that it does. Anyone have experience as to whether it helps immersiveness (less "I make a stealth check" instead of describing hiding?), or whether people have tried this system more DM-facing or PC-facing?