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I think what would be a good start is by first checking your clients site.  This would also probably be the most cost efficient method in finding out, however take longer. You could potentially check  (depending on availability): keyword traffic for users entering domain.com vs not domain.com phrases. Use a data range over 3-6 months and compare that to the same period last year. If your clients have email and social tracking enable on their site compare this keyword traffic for the above phrases. Otherwise you would probably have to approach research analyst or competitive intelligence companies i.e. Hitwise or Citi Investment Research and Analysis. Read a post on SEL today here's the link -http://searchengineland.com/google-still-1-traffic-source-for-most-of-top-30-websites-report-110410 If they can get this type of data, I don't see why they cannot get other types of consumer behaviour data. Hope this helps, Vahe

Hmm, I definitely think there is a page level element but Google have gone on record to say there's also a domain level impact. I imagine that the definition Google holds of a "site" is used in this case rather than slapping the whole domain.

EGOLS video has a good idea at its heart buts it fails for me because its about 10x too long - 15 seconds is all you need to show that concept I bet it lost a ton of its potential reach due to its length before payoff - the client lost out due to the agency's ego

How about Rich Snippets?