I couldn't agree more with the moral of the vector/array optimization story (above).
You should never guess at what your performance bottlenecks are. I can't even count the times the dev team was sure that the problem was some one thing, then we profile, and see that it was something completely different. Often the problems aren't the major stuff, but little things.
Don't waste your time, or let others, optimizing code without clear evidence of what is slow. (go buy TrueTime of Quantify!)
PROFILE! PROFILE! PROFILE!