Have you tried feigning death? That works only if whoever is blathering on is socially adept enough to realize one or more members of his (or her) audience has collapsed into a heap on the floor. (I.e., rarely.) Another strategy, but one that takes some advance planning, is to take out a bag of marbles and empty it on the conference table. Management and marketing types will be so distracted by the shiny baubles that you can safely sneak out and do some actual work.
author and iconoclast