Rogues can be a lot of fun and very powerful / flexible.
The problem with a Warrior/Rogue is that the Warrior skills start to really take over. They have a set cooldown regardless of what weapon you use, and get the best bonus from the highest damage weapon you can wield. Positioning is also important, because you want to get the most number of people in range of your whirlwind, but that is usually not a good backstabbing position.
Warrior skills also tend to have slightly higher strength requirements, and Strength does not contribute to the accuracy of daggers and rapiers.
