smallcompany - 4:59 pm on May 31, 2012 (gmt 0)
I guarantee that one well-focused hour of negative keyword research would save enough money over time to be well worth the effort.
For this type of research, I create an ad group with either phrase or broad+ match (or both), and I check search terms from time to time. This helps with constant negative keyword addition. It also helps in discovering new potentials that can be put into exact match in other ad groups.