Wow, lots of vassal-takers I see.

What campaign difficulty are you all playing on? I usually play H or VH, so that might have something to do with the rarity of ceasefires or vassals in my games.

It seems you're all getting your vassals well into the game -- not too late, but not too early.

Some good ideas here, and some things I hadn't thought about. Particularly the bit about making sure your target is at war with other factions. Guess I'll have to just play around a bit more...