CHARACTER SKILL ROLLS
Unless I specifically ask for one I will do all the "soft" skill rolls for the characters. You can ask for one in particular situations, but I'll roll the checks in certain situations even if you don't ask.
The reason for this is that, for these "soft" skill rolls, you shouldn't know how well you did. For example, if you roll a "3" on perception you know that if something's out there you probably didn't spot it, and conversely if you roll a "20" you can be pretty confident that you saw everything there is to see. If you roll a "20" on a Knowledge check you're pretty certain you know everything there is to know on the subject. But a low roll means you need to keep searching. The way I do it puts you in the same position as your character . . . you see what you see, know what you know, and sense what you sense, but you don't really have a solid idea if you might have missed something.
Same thing goes for Sense Motive, Stealth, and other skill rolls.
Skills like Acrobatics, Jump, Climb, and Swim, on the other hand, are "hard" skills; they have immediate up-or-down results for your character. You either avoid AoOs or you don't. You stay balanced on the beam or you don't. You jump the chasm or you don't. You successfully push the animal or you don't. You perform a feat of horseback riding or you don't. So in those cases you should roll the check for the character because the character immediately knows how well they did.
List of Skills That Are Generally "Soft," and That I Therefore Roll:
Appraise
Bluff
Diplomacy
Disguise
Intimidate
Knowledge (All)
Perception
Sense Motive
Sleight of Hand
Stealth
List of Skills That Are Generally "Hard," and That You Therefore Roll:
Acrobatics
Climb
Craft
Escape Artist
Fly
Handle Animal
Heal
Profession
Ride
Swim
Use Magic Device
Hybrid Skills (Classification Depends on the Particular Use):
Linguistics
Perform
Spellcraft
Survival