The SRD clearly states that incorporeal creatures have no Strength score, and use their Dexterity modifier for both melee and ranged attacks. However, what about Strength-based skills? Can a spook even use skills like Jump? Do they get a bonus from Strength (+0) or does Dexterity replace it?
From the SRD:
The modifier for a nonability is +0.
The incorporeal subtype makes no mention of exceptions for strength-based skills, so in the absence of any text to the contrary (such as exists for melee attacks), you simply use your strength modifier (+0) for any strength-based skill checks you make.