I dont, specifically becuase i only worry about marketing my product(s) instead of trying to steal traffic or work around someone elses. I suppose if you were trying to break in, you could cross reference against some competitors, but the Google keyword tool will give you similar info like traffic volume and competition anyway.
The downside of these is you're going to have to test every keyword anyway, so why not just use your brain and the free adwords keyword tool instead? By all means, use these tools for brainstorming, but "stealing winning keywords" is rubbish. Your account and the account of the person you're trying to rip off are not going to be identical. They could be paying $0.05 for their spot while you'd have to pay $1.00 maybe. It's all hype and preying on the people who are on the never ending search for the magic pill and are trying to find every short cut they can.