As a current CAT-2 rocking the CBT thing once again, they aren't entirely useless. As long as you're bouncing them off NATOPS/NATIP/your instructors they can be a great resource. Hell, today I did one that left me wondering where the hell was this when I was an upgrading TACCO!?!??! The plus side of CBTs is that they can make the blue sleeping pill digestible. The downside is that they can make you more inclined to just use them for aircraft knowledges rather than the source documents. Moral of the story, powerpoints/CBTs can make you want to gouge your eyes out, but used correctly can be effective.