Study Finds Small Businesses Waste 25 Percent Of Their PPC Budgets

Good article from Search Engine Land...
I would say that this is a conservative number, but defiantly real.
AND that's just at the "gross", click level not counting conversion rates, not enough budget or keywords to work with and the inherent inefficiency of a single search engine/platform concentration

Study Finds Small Businesses Waste 25 Percent Of Their PPC Budgets