Alchemist - Only to be capable of using alchemy skill + spell.
Priest - Only capable to bless weapons (all other classes however can still pray.)
Barbarian - Only class capable of using woodlore (id organics.)
Warrior - Only class capable of using smithery (id weapons.)
Thief - Only class capable of stealing.
Definately would distiguish classes, majorly encourage player co-orperation (along with a need for each class in kingdoms) and the economy as players could pay for their services.
__________________ "Make the *dreams* of today the *opportunities* of tomorrow."