Pale Master increases caster level by 1 at each odd level (as per wizard's spell level progression) and also provide new spells to sorcerer/bard
after becoming the Pale Master, character's alignment is shifted to Lawful Evil. Character with levels in PM won't be able to change alignment by any means.
Can't take epic spells, unless you can cast 9.level spells. (19int/wisdom + spellcasting class with 9.level spells)