How would you revise Thieves to be more Old School?

[True Black Raven]

How would you revise Thieves to be more Old School? By that I mean get rid of the percentages and nail down the difference between a thief attempting something and all other classes attempting the same thing. Or are Thieves inherently broken by the implication that they can do things that no other player gets to do.

[arjen]

Using the "skills as saving throw method", all PC can try whatever but if there is a chance if a bad result or a check to succeed (6in d6) a thief can make an extra roll (a save if you will) to succeed or avoid bad results (with a 4 or 5+ on a d6 for instance)

[hengest]

Rename and repower Thieves. A semi-class, PC-friendly, but "between" regular classes and the non-powered normals.

Minimal advancement within game system. Perhaps only three broad "levels":

Chops
Pro
Old Master


Sneak

Morally flexible (i.e. - the abilities on their own are neither criminal nor evil). 

Disappearing act.
Forgettable.
Somewhat mechanically inclined.
Inclined to tactical unpredictability in close combat.

All attributable to a central feature of these people: they are differently oriented to space, physical and social. Most people imagine space and surrounding objects "changing" around their person as they move about. They see themselves "inside" space. Sneaks see social and physical space as if from the outside and are more able to exploit its hidden features.

They do not do well in hierarchical organizations or under military discipline.