I love bribery, once I have the cash! It's the best way to deal with those BIG enemy empires that are beginning to bloat... where possible, I use spies to soften things up, exposing any secret vices etc first, and if necessary invade the general's province so he loses his title at the point my emissary arrives. Another good tip is to find where recently ransomed armies have been returned... once they are available to command again they are also available to bribe, usually still pretty disloyal after a sound beating. Naval blockades also help to reduce loyalty by isolating either the enemy king, or your bribe target.