Man I was a master of substitution a year ago - now I just feel like shit whenever I catch myself doing it. It's the avoidance tactic that I'm working on stopping the most. You definitely cannot always get away with it; several people have mentioned names and addresses. It just leads to even more anticipation, wasted energy and fear in the long run. It feels great when you've skirted another moment of potential disfluency, but it's gonna bite you in the ass eventually.