I tried to brainstorm uses for core rulebook skills. Some of these have been mentioned in other threads and some descriptions are directly from the core rulebook. I've added a few extra notes too. Of course all skills are tied to an attribute and contribute to it's increase while trained. I mostly tried to think PC to PC interaction. There are some awesome ideas on these forums.
It would seem a fail if all passive skills could be maxed during character advancement, so I would suggest a max number of skill points that could be changed with action bar build, don't know though how this is handled to avoid uniformed characters, maybe through armor.
Acrobatics - dodging attacks of opportunity, tumbling like in DDO(ie. while tumbling less damage from AoE spells), jump distance, falling, crossing narrow surfaces, hindered by armor
Appraise - better NPC prices,
Bluff - feint in combat(decrease damage resistance of opponent), a successful Bluff check can give you the momentary diversion you need to attempt a Stealth check while people are aware of you
Climb - climbing castle walls, cliffs, ability to use climbing hook and rope, climbing speed, hindered by armor
Craft - alchemy, armor, baskets, books, bows, calligraphy, carpentry, cloth, clothing, glass, jewelry, leather, locks, paintings, pottery, sculptures, ships, shoes, stonemasonry, traps, and weapons.
Diplomacy - organizing settlements, more settlement options/buildings/bonuses, gain reputation faster with NPC factions(could also have some bonuses from switching from one NPC faction to another)
Disable Device - disarm traps, open locks, sabotage siege engines, hindered by armor
Disguise - entering a settlement your'e not normally allowed(disguising alignment and race), would require gear
Escape Artist - escaping from some movement hindering net, traps, spells and grapple. Move through tight space. Hindered by armor.
Fly - manouvering in air, flying speed
Handle Animal - tame wild animal(companion), get a wild animal to defend you or leave you alone
Heal - heal debuffs caused by critical hits, small amount of hit points, poison, disease, self or other
Intimidate - cause debuff in combat, organizing settlements, more settlement options/buildings/bonuses
Knowledge - information on monsters weaknesses, characters, settlements, buildings, ore, skins, trees, etc quality of materials, could be tied to profession and crafting
Linguistics - learn languages, secret languages/signs, write books and scrolls, decipher languages/text
Perception - discover disguise, discover stealthed characters, traps, get PVE alerts/notices in wilderness, discover pick pocketing
Perform - play instrument, dance, sing, gain small amounts of money from commoners
Profession - architect, baker, barrister, brewer, butcher, clerk, cook, courtesan, driver, engineer, farmer, fisherman, gambler, gardener, herbalist, innkeeper, librarian, merchant, midwife, miller, miner, porter, sailor, scribe, shepherd, stable master, soldier, tanner, trapper, and woodcutter.
Ride - mount speed and armor, how to stay in saddle while attacked
Sense Motive - oppose Bluff, gain information on certain enchanment spells being cast/active
Sleight of Hand - pick pocket, cheating in cards, hindered by armor
Spellcraft - information what spell is being cast by opponent, Learn a spell from a spellbook or scroll, scribe a spell to scroll or book, decipher a scroll
Stealth - decreasing other characters view distance to see the character stealthing, hindered by armor
Survival - enemy list/bounty contract tracking(arrow and dot on map), cooking in wilderness, ignore weather effects
Swim - swim/diving speed and breath longevity, hindered by armor
Use Magic Device - use magic device that needs another race, class, or alignment to activate
Some of the skills could be used in synergy with weapon skills to gain bonuses etc. ie. sneak attack and sleight of hand etc.