alexsel - 5:13 pm on Nov 22, 2011 (gmt 0)
Absolutely. The negative keywords list is essential if your running a lot of broad match/modifier keywords. You would be shocked to see some of the search queries Google matches your keyword to.
Once you get started with this process, keep the broad match on for as long as you can. Because of seasonality and trends, new search queries will pop up every week, giving you great insight into what people are really looking for, gleaning insights from what keywords produce positive ROI and getting rid of the ones that don't. It's also a great opportunity to structure your campaigns/ad groups into more tighter themes.