Considering the recent litigation in which Google apparently claimed that all the emails, all the data in them, are Google's property and can do with the data whatever they want, I get frequent questions from our employees how does this translate into Gmail for business which we're using. Is the data in our corporate account also Google's property?
Send your employees to Google's Gmail for business benefits page. http://www.google.com/enterprise/apps/business/benefits.html?#security It says "When you put your data in Google Apps, you still own it, and it says just that in our contracts."
If you're not encrypting your email, then you really can't be said to have any expectation of email privacy, so the flap about whether or not they scan your emails makes little sense to me. That email is scanned at every step of its journey, by various virus and spam scanners.
Google claims various rights regarding your content in their TOS, but the inherent copyrights, etc. stay with you. I've worked with Fortune 500 companies whose email was put through Google specifically because they could be relied on to keep it (it vastly simplifies SOX compliance, for example).
But if you're really worried about privacy, email is not the best medium.