Camarath said:
Thats true but a full rogue could also get +11/+11/+11/+6/+6/+4/+4 using Rapid Shot and GTWF which would be the same sneak attack damage (70d6). One level of monk would only add 1 attack (possible 10d6) and would give a -2 to all attacks and prevent the character from using armor. Since the rogue can dish out that much damage through other means I don't see Flurry of Blows as the cause of this problem.
Then add a level of monk on top of that. If everthing stacks, the damage just keeps growing. If it doesn't stack, you can get to the same damage potential by various means.