Marshall - 3:00 am on Aug 9, 2012 (gmt 0)
Blending email information into general search results could raise privacy worries. Google is trying to mitigate that by showing Gmail results in a collapsed format that users must open to see the details. For now, users must sign up to participate.
I do not have a gmail account, and regardless how they might scan the emails, I would not want Google or anyone else searching through them for any reason. I see major lawsuits coming out of this even if you have to sign up for it.