We're not the only ones trying to assign statistics to lead sourcing. But this thought popped into my head, and was validated by the aforementioned client CEO: if your company tracks incoming hits to the website (using WebTrends or a similar service), you'll likely see plenty of hits coming in from search engines like Google. You'll also see the search terms used.
For example, if you work at Widgets-R-Us, some of the search terms will be of the "what is a widget?" and "widget makers" variety. But could you, should you count inbound website visits that come from SPECIFIC searches for "Widgets-R-Us" as PR generated? Doesn't this speak to "brand awareness"?