Check this out:
http://www.davidnaylor.co.uk/archive...adsense-sites/
Adwords advertisers will be able to block low or non-converting sites. This will be rolled out to all Adwords advertisers soon.
As Dave suggests, even if your site manages to send genuine leads, you might be out of luck if the brand and marketing people don't want to be associated with your site.
This should have an upside if you're sending good traffic, however. It may see your payouts increased.