On Mon, 26 Mar 2012, Mark Rogers wrote:
An advert for an ERP package is more useful than an advert for (for example) new shoes[*], which makes the advert more valuable, and Google should need to shove fewer of them in my face to cover its costs (and make a profit) than otherwise would be the case. Do I believe that any humans are reading my private email? No I don't
You're probably right that they _don't_, at least not now. But be aware that they _can_, and you'd have no legal redress, because whatever Google do with your e-mail text, they do outside the UK, where the Data Protection Act and the Regulation of Investigatory Powers Act don't apply. And the idea that, by being outside the UK, they might do things that would violate UK law, is not just a hypothetical: I'm pretty sure that the targetted advertising based on e-mail text would be unlawful under section 1(3) of RIPA if the servers on which they did it were over here.
And then, as Chris said, you have your own legal responsibilities to consider. If, in the course of your business activities, you hand over someone else's personal information to Google without obtaining a "safe harbour agreement", whereby Google promise to treat those data as if they were bound by UK law, then you will almost certainly be in breach of DPA (IIRC, it's called the "eighth data protection principle").